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**Understand Big Tech Question Preferences and Variants**: Visit the [variants](https://github.com/0voice/Awesome-BigTech-Algorithms/blob/main/variants/README.md) folder.\n- **Self-Practice**: Refer to the [Practice Platforms](#-practice-platforms) below.\n\n### Big Tech Practice Navigation\n- [ByteDance](#bytedance)\n- [Alibaba](#alibaba)\n- [Tencent](#tencent)\n- [Meituan](#meituan)\n- [Baidu](#baidu)\n- [JD.com](#jdcom)\n- [Huawei](#huawei)\n- [Xiaomi](#xiaomi)\n- [Didi](#didi)\n- [Ctrip](#ctrip)\n- [Bilibili](#bilibili)\n- [Kuaishou](#kuaishou)\n- [Microsoft](#microsoft)\n- [Google](#google)\n- [Amazon](#amazon)\n- [Pinduoduo](#pinduoduo)\n- [Xiaohongshu](#xiaohongshu)\n- [miHoYo](#mihoyo)\n- [Vivo](#vivo)\n- [OPPO](#oppo)\n- [Ant Group](#ant-group)\n- [iFlytek](#iflytek)\n- [Meta](#meta)\n\n### ByteDance\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Valid Anagram | Hash Table, String | Easy | Medium | [LeetCode 242](https://leetcode.cn/problems/valid-anagram/) |\n| Fizz Buzz | Math, String | Easy | Low | [LeetCode 412](https://leetcode.cn/problems/fizz-buzz/) |\n| Reverse String | Array, Two Pointers | Easy | Low | [LeetCode 344](https://leetcode.cn/problems/reverse-string/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.cn/problems/valid-parentheses/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.cn/problems/reverse-linked-list/) |\n| Merge Two Sorted Lists | Linked List, Recursion | Easy | Medium | [LeetCode 21](https://leetcode.cn/problems/merge-two-sorted-lists/) |\n| Remove Element | Array, Two Pointers | Easy | Medium | [LeetCode 27](https://leetcode.cn/problems/remove-element/) |\n| Best Time to Buy and Sell Stock | Array, Dynamic Programming | Easy | High | [LeetCode 121](https://leetcode.cn/problems/best-time-to-buy-and-sell-stock/) |\n| Reverse Integer | Math | Easy | Medium | [LeetCode 7](https://leetcode.cn/problems/reverse-integer/) |\n| Palindrome Number | Math | Easy | Medium | [LeetCode 9](https://leetcode.cn/problems/palindrome-number/) |\n| Roman to Integer | Hash Table, String | Easy | Low | [LeetCode 13](https://leetcode.cn/problems/roman-to-integer/) |\n| Contains Duplicate | Array, Hash Table | Easy | High | [LeetCode 217](https://leetcode.cn/problems/contains-duplicate/) |\n| Majority Element | Array, Divide and Conquer | Easy | High | [LeetCode 169](https://leetcode.cn/problems/majority-element/) |\n| Linked List Cycle | Linked List, Two Pointers | Easy | Medium | [LeetCode 141](https://leetcode.cn/problems/linked-list-cycle/) |\n| Climbing Stairs | Dynamic Programming | Easy | High | [LeetCode 70](https://leetcode.cn/problems/climbing-stairs/) |\n| Remove Duplicates from Sorted List | Linked List | Easy | Low | [LeetCode 83](https://leetcode.cn/problems/remove-duplicates-from-sorted-list/) |\n| Search a 2D Matrix | Array, Binary Search | Medium | Medium | [LeetCode 74](https://leetcode.cn/problems/search-a-2d-matrix/) |\n| Add Two Numbers | Linked List, Math | Medium | High | [LeetCode 2](https://leetcode.cn/problems/add-two-numbers/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.cn/problems/longest-substring-without-repeating-characters/) |\n| Number of Islands | Depth-First Search, Breadth-First Search, Union Find | Medium | High | [LeetCode 200](https://leetcode.cn/problems/number-of-islands/) |\n| Maximum Subarray | Array, Divide and Conquer, Dynamic Programming | Medium | High | [LeetCode 53](https://leetcode.cn/problems/maximum-subarray/) |\n| Unique Paths | Dynamic Programming | Medium | Medium | [LeetCode 62](https://leetcode.cn/problems/unique-paths/) |\n| Generate Parentheses | Backtracking | Medium | High | [LeetCode 22](https://leetcode.cn/problems/generate-parentheses/) |\n| Remove Nth Node From End of List | Linked List, Two Pointers | Medium | High | [LeetCode 19](https://leetcode.cn/problems/remove-nth-node-from-end-of-list/) |\n| Letter Combinations of a Phone Number | Backtracking, String | Medium | Medium | [LeetCode 17](https://leetcode.cn/problems/letter-combinations-of-a-phone-number/) |\n| 3Sum | Array, Two Pointers | Medium | High | [LeetCode 15](https://leetcode.cn/problems/3sum/) |\n| Permutations | Backtracking | Medium | High | [LeetCode 46](https://leetcode.cn/problems/permutations/) |\n| Combination Sum | Backtracking | Medium | High | [LeetCode 39](https://leetcode.cn/problems/combination-sum/) |\n| Group Anagrams | Array, Hash Table, String | Medium | Medium | [LeetCode 49](https://leetcode.cn/problems/group-anagrams/) |\n| Merge Intervals | Array, Sorting | Medium | High | [LeetCode 56](https://leetcode.cn/problems/merge-intervals/) |\n| Subsets | Bit Manipulation, Backtracking | Medium | Medium | [LeetCode 78](https://leetcode.cn/problems/subsets/) |\n| Word Search | Array, Backtracking, Matrix | Medium | Low | [LeetCode 79](https://leetcode.cn/problems/word-search/) |\n| Validate Binary Search Tree | Tree, Depth-First Search | Medium | Medium | [LeetCode 98](https://leetcode.cn/problems/validate-binary-search-tree/) |\n| Construct Binary Tree from Preorder and Inorder Traversal | Tree, Array, Hash Table, Divide and Conquer | Medium | Medium | [LeetCode 105](https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) |\n| Longest Consecutive Sequence | Union Find, Array, Hash Table | Medium | High | [LeetCode 128](https://leetcode.cn/problems/longest-consecutive-sequence/) |\n| Word Break | Dynamic Programming, Memoization | Medium | Medium | [LeetCode 139](https://leetcode.cn/problems/word-break/) |\n| Restore IP Addresses | String, Backtracking | Medium | Medium | [LeetCode 93](https://leetcode.cn/problems/restore-ip-addresses/) |\n| LRU Cache | Hash Table, Doubly Linked List, Design | Medium | High | [LeetCode 146](https://leetcode.cn/problems/lru-cache/) |\n| Valid Sudoku | Array, Hash Table, Backtracking, Matrix | Medium | Low | [LeetCode 36](https://leetcode.cn/problems/valid-sudoku/) |\n| Two Sum II - Input Array Is Sorted | Array, Two Pointers | Medium | Medium | [LeetCode 167](https://leetcode.cn/problems/two-sum-ii-input-array-is-sorted/) |\n| String to Integer (atoi) | String | Medium | Low | [LeetCode 8](https://leetcode.cn/problems/string-to-integer-atoi/) |\n| Container With Most Water | Array, Two Pointers | Medium | High | [LeetCode 11](https://leetcode.cn/problems/container-with-most-water/) |\n| Minimum Size Subarray Sum | Array, Prefix Sum, Two Pointers | Medium | Medium | [LeetCode 209](https://leetcode.cn/problems/minimum-size-subarray-sum/) |\n| Next Permutation | Array | Medium | Medium | [LeetCode 31](https://leetcode.cn/problems/next-permutation/) |\n| Spiral Matrix | Array, Matrix | Medium | Low | [LeetCode 54](https://leetcode.cn/problems/spiral-matrix/) |\n| Search in Rotated Sorted Array | Array, Binary Search | Medium | High | [LeetCode 33](https://leetcode.cn/problems/search-in-rotated-sorted-array/) |\n| Minimum Path Sum | Array, Dynamic Programming, Matrix | Medium | Medium | [LeetCode 64](https://leetcode.cn/problems/minimum-path-sum/) |\n| Redundant Connection | Depth-First Search, Breadth-First Search, Union Find, Graph | Medium | Low | [LeetCode 684](https://leetcode.cn/problems/redundant-connection/) |\n| Longest Mountain in Array | Array | Medium | Low | [LeetCode 845](https://leetcode.cn/problems/longest-mountain-in-array/) |\n| Count Nice Pairs in an Array | Hash Table, String, Counting | Medium | Low | [LeetCode 1815](https://leetcode.cn/problems/count-nice-pairs-in-an-array/) |\n| Subarray Sum Equals K | Array, Hash Table, Prefix Sum | Medium | High | [LeetCode 560](https://leetcode.cn/problems/subarray-sum-equals-k/) |\n| Longest Palindromic Substring | String, Dynamic Programming | Medium | High | [LeetCode 5](https://leetcode.cn/problems/longest-palindromic-substring/) |\n| Binary Tree Level Order Traversal | Tree, Breadth-First Search, Binary Tree | Medium | Medium | [LeetCode 102](https://leetcode.cn/problems/binary-tree-level-order-traversal/) |\n| Course Schedule | Depth-First Search, Breadth-First Search, Graph, Topological Sort | Medium | Medium | [LeetCode 207](https://leetcode.cn/problems/course-schedule/) |\n| Kth Largest Element in an Array | Array, Heap, Divide and Conquer | Medium | High | [LeetCode 215](https://leetcode.cn/problems/kth-largest-element-in-an-array/) |\n| Product of Array Except Self | Array, Prefix Sum | Medium | High | [LeetCode 238](https://leetcode.cn/problems/product-of-array-except-self/) |\n| Longest Increasing Subsequence | Array, Dynamic Programming, Binary Search | Medium | High | [LeetCode 300](https://leetcode.cn/problems/longest-increasing-subsequence/) |\n| Partition Equal Subset Sum | Dynamic Programming, Knapsack | Medium | Medium | [LeetCode 416](https://leetcode.cn/problems/partition-equal-subset-sum/) |\n| Edit Distance | Dynamic Programming | Medium | Medium | [LeetCode 72](https://leetcode.cn/problems/edit-distance/) |\n| Sliding Window Maximum | Queue, Sliding Window, Heap | Hard | High | [LeetCode 239](https://leetcode.cn/problems/sliding-window-maximum/) |\n| Largest Component Size by Common Factor | Union Find, Array, Hash Table, Math | Hard | Low | [LeetCode 952](https://leetcode.cn/problems/largest-component-size-by-common-factor/) |\n| Making A Large Island | Depth-First Search, Breadth-First Search, Matrix | Hard | Low | [LeetCode 827](https://leetcode.cn/problems/making-a-large-island/) |\n| Median of Two Sorted Arrays | Array, Binary Search, Divide and Conquer | Hard | High | [LeetCode 4](https://leetcode.cn/problems/median-of-two-sorted-arrays/) |\n| Merge k Sorted Lists | Linked List, Divide and Conquer, Heap, Priority Queue | Hard | High | [LeetCode 23](https://leetcode.cn/problems/merge-k-sorted-lists/) |\n| Split Array Largest Sum | Array, Binary Search, Dynamic Programming | Hard | Medium | [LeetCode 410](https://leetcode.cn/problems/split-array-largest-sum/) |\n| Reverse Nodes in k-Group | Linked List, Recursion | Hard | High | [LeetCode 25](https://leetcode.cn/problems/reverse-nodes-in-k-group/) |\n| Profitable Schemes | Dynamic Programming | Hard | Medium | [LeetCode 879](https://leetcode.cn/problems/profitable-schemes/) |\n| Maximum Profit in Job Scheduling | Array, Binary Search, Dynamic Programming, Sorting | Hard | Medium | [LeetCode 1235](https://leetcode.cn/problems/maximum-profit-in-job-scheduling/) |\n| Trapping Rain Water | Stack, Array, Two Pointers, Dynamic Programming, Monotonic Stack | Hard | High | [LeetCode 42](https://leetcode.cn/problems/trapping-rain-water/) |\n| Minimum Window Substring | Hash Table, String, Sliding Window | Hard | High | [LeetCode 76](https://leetcode.cn/problems/minimum-window-substring/) |\n| Largest Rectangle in Histogram | Array, Stack, Monotonic Stack | Hard | High | [LeetCode 84](https://leetcode.cn/problems/largest-rectangle-in-histogram/) |\n| Binary Tree Maximum Path Sum | Tree, Depth-First Search, Dynamic Programming, Binary Tree | Hard | High | [LeetCode 124](https://leetcode.cn/problems/binary-tree-maximum-path-sum/) |\n\n### Alibaba\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Two Sum | Array, Hash Table | Easy | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Stack, String | Easy | Medium | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Climbing Stairs | Dynamic Programming, Memoization | Easy | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Best Time to Buy and Sell Stock | Array, Dynamic Programming | Easy | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Maximum Subarray | Array, Greedy | Easy | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Convert Sorted Array to Binary Search Tree | Tree, Depth-First Search | Easy | Medium | [LeetCode 108](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/) |\n| Minimum Depth of Binary Tree | Tree, Depth-First Search | Easy | Low | [LeetCode 111](https://leetcode.com/problems/minimum-depth-of-binary-tree/) |\n| Invert Binary Tree | Tree, Depth-First Search | Easy | High | [LeetCode 226](https://leetcode.com/problems/invert-binary-tree/) |\n| Path Sum | Tree, Depth-First Search | Easy | Medium | [LeetCode 112](https://leetcode.com/problems/path-sum/) |\n| Implement strStr() | String, Sliding Window | Easy | Low | [LeetCode 28](https://leetcode.com/problems/implement-strstr/) |\n| Search Insert Position | Array, Binary Search | Easy | Medium | [LeetCode 35](https://leetcode.com/problems/search-insert-position/) |\n| Maximum Depth of Binary Tree | Tree, Depth-First Search | Easy | Medium | [LeetCode 104](https://leetcode.com/problems/maximum-depth-of-binary-tree/) |\n| Kth Missing Positive Number | Array, Math | Easy | Low | [LeetCode 1539](https://leetcode.com/problems/kth-missing-positive-number/) |\n| Find Smallest Letter Greater Than Target | Array, Binary Search | Easy | Low | [LeetCode 744](https://leetcode.com/problems/find-smallest-letter-greater-than-target/) |\n| Longest Substring Without Repeating Characters | String, Two Pointers | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Number of Islands | Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Course Schedule | Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Coin Change | Dynamic Programming | Medium | High | [LeetCode 322](https://leetcode.com/problems/coin-change/) |\n| Decode String | Stack, Recursion | Medium | Medium | [LeetCode 394](https://leetcode.com/problems/decode-string/) |\n| Add Strings | String, Math | Medium | Low | [LeetCode 415](https://leetcode.com/problems/add-strings/) |\n| Find All Anagrams in a String | Hash Table, Sliding Window | Medium | Medium | [LeetCode 438](https://leetcode.com/problems/find-all-anagrams-in-a-string/) |\n| Diameter of Binary Tree | Tree, Depth-First Search | Medium | Medium | [LeetCode 543](https://leetcode.com/problems/diameter-of-binary-tree/) |\n| Daily Temperatures | Stack, Monotonic Stack | Medium | Medium | [LeetCode 739](https://leetcode.com/problems/daily-temperatures/) |\n| Partition Labels | Greedy, Two Pointers | Medium | Low | [LeetCode 763](https://leetcode.com/problems/partition-labels/) |\n| K Closest Points to Origin | Sorting, Heap | Medium | Low | [LeetCode 973](https://leetcode.com/problems/k-closest-points-to-origin/) |\n| Merge k Sorted Lists | Linked List, Divide and Conquer | Medium | Medium | [LeetCode 23](https://leetcode.com/problems/merge-k-sorted-lists/) |\n| Longest Valid Parentheses | Stack, Dynamic Programming | Medium | Medium | [LeetCode 32](https://leetcode.com/problems/longest-valid-parentheses/) |\n| Jump Game | Greedy | Medium | Medium | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Unique Paths | Dynamic Programming | Medium | Medium | [LeetCode 62](https://leetcode.com/problems/unique-paths/) |\n| Course Schedule II | Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 210](https://leetcode.com/problems/course-schedule-ii/) |\n| Lowest Common Ancestor of a Binary Tree | Tree, Depth-First Search | Medium | High | [LeetCode 236](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) |\n| Custom Sort String | String, Greedy | Medium | Low | [LeetCode 791](https://leetcode.com/problems/custom-sort-string/) |\n| 3Sum | Array, Two Pointers | Medium | High | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Find Duplicate Subtrees | Tree, Hash Table | Medium | Low | [LeetCode 652](https://leetcode.com/problems/find-duplicate-subtrees/) |\n| Validate Binary Search Tree | Tree, Depth-First Search | Medium | High | [LeetCode 98](https://leetcode.com/problems/validate-binary-search-tree/) |\n| Construct Binary Tree from Preorder and Inorder Traversal | Tree, Array | Medium | Medium | [LeetCode 105](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) |\n| Construct Binary Tree from Inorder and Postorder Traversal | Tree, Array | Medium | Medium | [LeetCode 106](https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/) |\n| Kth Smallest Element in a BST | Tree, Depth-First Search | Medium | Medium | [LeetCode 230](https://leetcode.com/problems/kth-smallest-element-in-a-bst/) |\n| Path Sum II | Tree, Depth-First Search | Medium | Medium | [LeetCode 113](https://leetcode.com/problems/path-sum-ii/) |\n| Binary Tree Right Side View | Tree, Depth-First Search | Medium | Medium | [LeetCode 199](https://leetcode.com/problems/binary-tree-right-side-view/) |\n| Partition Equal Subset Sum | DP, Subset Sum | Medium | High | [LeetCode 416](https://leetcode.com/problems/partition-equal-subset-sum/) |\n| Can I Win | DP, State Compression | Medium | Low | [LeetCode 464](https://leetcode.com/problems/can-i-win/) |\n| Maximum Sum Circular Subarray | Probability, DP | Medium | Low | [LeetCode 918](https://leetcode.com/problems/maximum-sum-circular-subarray/) |\n| Stone Game II | Game Theory, Greedy, Array | Medium | Low | [LeetCode 1140](https://leetcode.com/problems/stone-game-ii/) |\n| Count Primes | Simulation, Sieve of Eratosthenes | Medium | Medium | [LeetCode 204](https://leetcode.com/problems/count-primes/) |\n| House Robber III | DP, Tree Structure | Medium | Low | [LeetCode 337](https://leetcode.com/problems/house-robber-iii/) |\n| Convert BST to Greater Tree | Tree, Depth-First Search | Medium | Low | [LeetCode 538](https://leetcode.com/problems/convert-bst-to-greater-tree/) |\n| Clone Graph | Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 133](https://leetcode.com/problems/clone-graph/) |\n| Pacific Atlantic Water Flow | Depth-First Search | Medium | Low | [LeetCode 417](https://leetcode.com/problems/pacific-atlantic-water-flow/) |\n| LRU Cache | Design, Hash Table | Medium | High | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Min Stack | Stack, Design | Medium | High | [LeetCode 155](https://leetcode.com/problems/min-stack/) |\n| Next Permutation | Array, Two Pointers | Medium | High | [LeetCode 31](https://leetcode.com/problems/next-permutation/) |\n| Combination Sum II | Array, Backtracking | Medium | Medium | [LeetCode 40](https://leetcode.com/problems/combination-sum-ii/) |\n| Find Bottom Left Tree Value | Tree, Depth-First Search, Breadth-First Search | Medium | Low | [LeetCode 513](https://leetcode.com/problems/find-bottom-left-tree-value/) |\n| Maximum Length of Repeated Subarray | Array, Hash Table, String Matching | Medium | Low | [LeetCode 718](https://leetcode.com/problems/maximum-length-of-repeated-subarray/) |\n| 3Sum Closest | Array, Two Pointers | Medium | Medium | [LeetCode 16](https://leetcode.com/problems/3sum-closest/) |\n| Letter Combinations of a Phone Number | Backtracking, String | Medium | Medium | [LeetCode 17](https://leetcode.com/problems/letter-combinations-of-a-phone-number/) |\n| Generate Parentheses | Backtracking | Medium | High | [LeetCode 22](https://leetcode.com/problems/generate-parentheses/) |\n| Find First and Last Position of Element in Sorted Array | Array, Binary Search | Medium | Medium | [LeetCode 34](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) |\n| Jump Game II | Array, Greedy | Medium | Medium | [LeetCode 45](https://leetcode.com/problems/jump-game-ii/) |\n| Group Anagrams | Array, Hash Table, String | Medium | High | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Merge Intervals | Array, Sorting | Medium | High | [LeetCode 56](https://leetcode.com/problems/merge-intervals/) |\n| Subsets | Bit Manipulation, Backtracking | Medium | Medium | [LeetCode 78](https://leetcode.com/problems/subsets/) |\n| Binary Tree Level Order Traversal | Tree, Breadth-First Search | Medium | High | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Kth Largest Element in an Array | Array, Heap, Divide and Conquer | Medium | High | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| Remove Nth Node From End of List | Linked List, Two Pointers | Medium | Medium | [LeetCode 19](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) |\n| Search in Rotated Sorted Array | Array, Binary Search | Medium | Medium | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Reverse Nodes in k-Group | Linked List, Recursion | Medium | Medium | [LeetCode 25](https://leetcode.com/problems/reverse-nodes-in-k-group/) |\n| Trapping Rain Water | Stack, Two Pointers | Hard | High | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| Serialize and Deserialize Binary Tree | Tree, Depth-First Search | Hard | Low | [LeetCode 297](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) |\n| Count Vowels Permutation | Digit DP, Knapsack | Hard | Low | [LeetCode 1220](https://leetcode.com/problems/count-vowels-permutation/) |\n| Sliding Window Maximum | Simulation, Priority Queue | Hard | High | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Binary Tree Maximum Path Sum | Tree, Depth-First Search | Hard | High | [LeetCode 124](https://leetcode.com/problems/binary-tree-maximum-path-sum/) |\n| Word Ladder | Breadth-First Search, String | Hard | Medium | [LeetCode 127](https://leetcode.com/problems/word-ladder/) |\n| Word Ladder II | Breadth-First Search, String | Hard | Low | [LeetCode 126](https://leetcode.com/problems/word-ladder-ii/) |\n| Profitable Schemes | Array, Dynamic Programming | Hard | Low | [LeetCode 879](https://leetcode.com/problems/profitable-schemes/) |\n| Regular Expression Matching | String, Dynamic Programming | Hard | Medium | [LeetCode 10](https://leetcode.com/problems/regular-expression-matching/) |\n\n### Tencent\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Two Sum | Array, Hash Table | Easy | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Linked List Cycle | Linked List, Two Pointers | Easy | High | [LeetCode 141](https://leetcode.com/problems/linked-list-cycle/) |\n| Climbing Stairs | Dynamic Programming, Memoization | Easy | High | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Assign Cookies | Greedy, Sorting | Easy | High | [LeetCode 455](https://leetcode.com/problems/assign-cookies/) |\n| Best Time to Buy and Sell Stock II | Array, Dynamic Programming | Easy | High | [LeetCode 122](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/) |\n| Binary Search | Array, Binary Search | Easy | High | [LeetCode 704](https://leetcode.com/problems/binary-search/) |\n| Intersection of Two Linked Lists | Linked List, Two Pointers | Easy | High | [LeetCode 160](https://leetcode.com/problems/intersection-of-two-linked-lists/) |\n| Complex Number Multiplication | Math, String | Easy | Medium | [LeetCode 537](https://leetcode.com/problems/complex-number-multiplication/) |\n| Number of Islands | Depth-First Search, Breadth-First Search | Medium | High | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Course Schedule | Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Coin Change | Dynamic Programming | Medium | High | [LeetCode 322](https://leetcode.com/problems/coin-change/) |\n| Unique Paths | Dynamic Programming | Medium | High | [LeetCode 62](https://leetcode.com/problems/unique-paths/) |\n| Daily Temperatures | Stack, Monotonic Stack | Medium | High | [LeetCode 739](https://leetcode.com/problems/daily-temperatures/) |\n| Generate Parentheses | Backtracking | Medium | High | [LeetCode 22](https://leetcode.com/problems/generate-parentheses/) |\n| Letter Combinations of a Phone Number | Backtracking, String | Medium | High | [LeetCode 17](https://leetcode.com/problems/letter-combinations-of-a-phone-number/) |\n| 3Sum | Array, Two Pointers | Medium | High | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Group Anagrams | Array, Hash Table, String | Medium | High | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Merge Intervals | Array, Sorting | Medium | High | [LeetCode 56](https://leetcode.com/problems/merge-intervals/) |\n| Task Scheduler | Greedy, Priority Queue | Medium | High | [LeetCode 621](https://leetcode.com/problems/task-scheduler/) |\n| Network Delay Time | Graph, Shortest Path | Medium | Medium | [LeetCode 743](https://leetcode.com/problems/network-delay-time/) |\n| Cheapest Flights Within K Stops | Graph, Depth-First Search | Medium | Medium | [LeetCode 787](https://leetcode.com/problems/cheapest-flights-within-k-stops/) |\n| Kth Largest Element in an Array | Array, Heap, Divide and Conquer | Medium | High | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| Longest Increasing Subsequence | Array, Dynamic Programming, Binary Search | Medium | High | [LeetCode 300](https://leetcode.com/problems/longest-increasing-subsequence/) |\n| Partition Equal Subset Sum | Dynamic Programming, Knapsack | Medium | Medium | [LeetCode 416](https://leetcode.com/problems/partition-equal-subset-sum/) |\n| Word Break | Dynamic Programming, Memoization | Medium | High | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Target Sum | Dynamic Programming, Knapsack | Medium | High | [LeetCode 494](https://leetcode.com/problems/target-sum/) |\n| Max Area of Island | Depth-First Search, Breadth-First Search | Medium | High | [LeetCode 695](https://leetcode.com/problems/max-area-of-island/) |\n| Container With Most Water | Array, Two Pointers | Medium | High | [LeetCode 11](https://leetcode.com/problems/container-with-most-water/) |\n| Valid Sudoku | Array, Hash Table, Backtracking | Medium | High | [LeetCode 36](https://leetcode.com/problems/valid-sudoku/) |\n| Number of Recent Calls | Design, Sliding Window | Medium | High | [LeetCode 933](https://leetcode.com/problems/number-of-recent-calls/) |\n| Design HashMap | Design, Hash Table | Medium | Medium | [LeetCode 706](https://leetcode.com/problems/design-hashmap/) |\n| Design Linked List | Design, Linked List | Medium | High | [LeetCode 707](https://leetcode.com/problems/design-linked-list/) |\n| Push Dominoes | Simulation, Queue | Medium | Low | [LeetCode 838](https://leetcode.com/problems/push-dominoes/) |\n| Implement Rand10() Using Rand7() | Math, Probability | Medium | High | [LeetCode 470](https://leetcode.com/problems/implement-rand10-using-rand7/) |\n| Sliding Window Maximum | Queue, Sliding Window, Heap | Hard | High | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Trapping Rain Water | Stack, Two Pointers | Hard | High | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| Binary Tree Maximum Path Sum | Tree, Depth-First Search | Hard | High | [LeetCode 124](https://leetcode.com/problems/binary-tree-maximum-path-sum/) |\n| Split Array Largest Sum | Binary Search, Dynamic Programming | Hard | Medium | [LeetCode 410](https://leetcode.com/problems/split-array-largest-sum/) |\n| Alien Dictionary | Graph, Topological Sort | Hard | Medium | [LeetCode 269](https://leetcode.com/problems/alien-dictionary/) |\n| Basic Calculator | Stack, Recursion | Hard | Medium | [LeetCode 224](https://leetcode.com/problems/basic-calculator/) |\n| Expression Add Operators | Backtracking, Dynamic Programming | Hard | Medium | [LeetCode 282](https://leetcode.com/problems/expression-add-operators/) |\n| Course Schedule III | Greedy, Priority Queue | Hard | Medium | [LeetCode 630](https://leetcode.com/problems/course-schedule-iii/) |\n| Maximum Profit in Job Scheduling | Array, Binary Search, Dynamic Programming | Hard | Medium | [LeetCode 1235](https://leetcode.com/problems/maximum-profit-in-job-scheduling/) |\n| Strong Password Checker | String, Greedy | Hard | Low | [LeetCode 420](https://leetcode.com/problems/strong-password-checker/) |\n| Sliding Puzzle | Breadth-First Search | Hard | Low | [LeetCode 773](https://leetcode.com/problems/sliding-puzzle/) |\n| Optimal Account Balancing | Graph, Shortest Path | Hard | Medium | [LeetCode 464](https://leetcode.com/problems/optimal-account-balancing/) |\n\n### Meituan\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Majority Element | Array, Divide and Conquer | Easy | High | [LeetCode 169](https://leetcode.com/problems/majority-element/) |\n| Complex Number Multiplication | Math, String | Easy | Medium | [LeetCode 537](https://leetcode.com/problems/complex-number-multiplication/) |\n| Path Sum III | Tree, Depth-First Search | Medium | High | [LeetCode 437](https://leetcode.com/problems/path-sum-iii/) |\n| Maximum Product Subarray | Array, Dynamic Programming | Medium | High | [LeetCode 152](https://leetcode.com/problems/maximum-product-subarray/) |\n| Sort Array By Parity II | Array, Two Pointers | Medium | High | [LeetCode 922](https://leetcode.com/problems/sort-array-by-parity-ii/) |\n| Range Sum Query - Mutable | Fenwick Tree, Segment Tree | Medium | High | [LeetCode 307](https://leetcode.com/problems/range-sum-query-mutable/) |\n| Implement Rand10() Using Rand7() | Math, Probability | Medium | High | [LeetCode 470](https://leetcode.com/problems/implement-rand10-using-rand7/) |\n| Number of Recent Calls | Design, Sliding Window | Medium | High | [LeetCode 933](https://leetcode.com/problems/number-of-recent-calls/) |\n| Design HashMap | Design, Hash Table | Medium | High | [LeetCode 706](https://leetcode.com/problems/design-hashmap/) |\n| Design Linked List | Design, Linked List | Medium | High | [LeetCode 707](https://leetcode.com/problems/design-linked-list/) |\n| Push Dominoes | Simulation, Queue | Medium | Medium | [LeetCode 838](https://leetcode.com/problems/push-dominoes/) |\n| Spiral Matrix II | Array, Math | Medium | High | [LeetCode 59](https://leetcode.com/problems/spiral-matrix-ii/) |\n| Max Area of Island | Depth-First Search, Breadth-First Search | Medium | Low | [LeetCode 695](https://leetcode.com/problems/max-area-of-island/) |\n| Course Schedule II | Graph, Depth-First Search | Medium | Medium | [LeetCode 210](https://leetcode.com/problems/course-schedule-ii/) |\n| Partition List | Linked List, Two Pointers | Medium | Low | [LeetCode 86](https://leetcode.com/problems/partition-list/) |\n| Decode Ways | Dynamic Programming | Medium | Medium | [LeetCode 91](https://leetcode.com/problems/decode-ways/) |\n| Daily Temperatures | Stack, Monotonic Stack | Medium | Medium | [LeetCode 739](https://leetcode.com/problems/daily-temperatures/) |\n| Interleaving String | String, Dynamic Programming | Medium | Low | [LeetCode 97](https://leetcode.com/problems/interleaving-string/) |\n| Subarray Sum Equals K | Array, Hash Table | Medium | Medium | [LeetCode 560](https://leetcode.com/problems/subarray-sum-equals-k/) |\n| Top K Frequent Words | Hash Table, Heap | Medium | Medium | [LeetCode 692](https://leetcode.com/problems/top-k-frequent-words/) |\n| 4Sum | Array, Two Pointers | Medium | Low | [LeetCode 18](https://leetcode.com/problems/4sum/) |\n| Decode String | Stack, String | Medium | Medium | [LeetCode 394](https://leetcode.com/problems/decode-string/) |\n| Zigzag Conversion | String | Medium | Low | [LeetCode 6](https://leetcode.com/problems/zigzag-conversion/) |\n| Fizz Buzz Multithreaded | Thread, Design | Medium | Low | [LeetCode 1195](https://leetcode.com/problems/fizz-buzz-multithreaded/) |\n| Longest Palindromic Subsequence | String, Dynamic Programming | Medium | Medium | [LeetCode 516](https://leetcode.com/problems/longest-palindromic-subsequence/) |\n| Odd Even Linked List | Linked List, Two Pointers | Medium | Low | [LeetCode 328](https://leetcode.com/problems/odd-even-linked-list/) |\n| Count of Range Sum | Array, Dynamic Programming | Hard | Low | [LeetCode 327](https://leetcode.com/problems/count-of-range-sum/) |\n| Wildcard Matching | String, Dynamic Programming | Hard | Low | [LeetCode 44](https://leetcode.com/problems/wildcard-matching/) |\n| Strong Password Checker | String, Greedy | Hard | High | [LeetCode 420](https://leetcode.com/problems/strong-password-checker/) |\n| Sliding Puzzle | Breadth-First Search | Hard | Medium | [LeetCode 773](https://leetcode.com/problems/sliding-puzzle/) |\n| Optimal Account Balancing | Graph, Shortest Path | Hard | High | [LeetCode 464](https://leetcode.com/problems/optimal-account-balancing/) |\n| Burst Balloons | Dynamic Programming, Interval | Hard | High | [LeetCode 312](https://leetcode.com/problems/burst-balloons/) |\n| Minimum Window Substring | Hash Table, Sliding Window | Hard | High | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n\n### Baidu\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Majority Element | Array, Divide and Conquer | Easy | High | [LeetCode 169](https://leetcode.com/problems/majority-element/) |\n| Search Insert Position | Array, Binary Search | Easy | High | [LeetCode 35](https://leetcode.com/problems/search-insert-position/) |\n| Binary Search | Array, Binary Search | Easy | High | [LeetCode 704](https://leetcode.com/problems/binary-search/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Maximum Subarray | Array, Divide and Conquer, Dynamic Programming | Easy | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Merge Two Sorted Lists | Linked List, Recursion | Easy | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Path Sum III | Tree, Depth-First Search | Medium | High | [LeetCode 437](https://leetcode.com/problems/path-sum-iii/) |\n| Maximum Product Subarray | Array, Dynamic Programming | Medium | High | [LeetCode 152](https://leetcode.com/problems/maximum-product-subarray/) |\n| Sort Array By Parity II | Array, Two Pointers | Medium | Medium | [LeetCode 922](https://leetcode.com/problems/sort-array-by-parity-ii/) |\n| Range Sum Query - Mutable | Fenwick Tree, Segment Tree | Medium | High | [LeetCode 307](https://leetcode.com/problems/range-sum-query-mutable/) |\n| Implement Rand10() Using Rand7() | Math, Probability | Medium | High | [LeetCode 470](https://leetcode.com/problems/implement-rand10-using-rand7/) |\n| Number of Recent Calls | Design, Sliding Window | Medium | High | [LeetCode 933](https://leetcode.com/problems/number-of-recent-calls/) |\n| Design HashMap | Design, Hash Table | Medium | High | [LeetCode 706](https://leetcode.com/problems/design-hashmap/) |\n| Design Linked List | Design, Linked List | Medium | High | [LeetCode 707](https://leetcode.com/problems/design-linked-list/) |\n| Push Dominoes | Simulation, Queue | Medium | Medium | [LeetCode 838](https://leetcode.com/problems/push-dominoes/) |\n| Search in Rotated Sorted Array | Array, Binary Search | Medium | High | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Find Minimum in Rotated Sorted Array | Array, Binary Search | Medium | High | [LeetCode 153](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/) |\n| Search a 2D Matrix | Array, Binary Search | Medium | High | [LeetCode 74](https://leetcode.com/problems/search-a-2d-matrix/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Array, Heap, Divide and Conquer | Medium | High | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| Longest Increasing Subsequence | Array, Dynamic Programming, Binary Search | Medium | High | [LeetCode 300](https://leetcode.com/problems/longest-increasing-subsequence/) |\n| String to Integer | String, Simulation | Medium | High | [LeetCode 8](https://leetcode.com/problems/string-to-integer-atoi/) |\n| Add Strings | String, Math | Medium | High | [LeetCode 415](https://leetcode.com/problems/add-strings/) |\n| LRU Cache | Hash Table, Doubly Linked List, Design | Medium | High | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Jump Game | Greedy | Medium | Medium | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Combination Sum II | Backtracking | Medium | Low | [LeetCode 40](https://leetcode.com/problems/combination-sum-ii/) |\n| Number of Longest Increasing Subsequence | Dynamic Programming | Medium | Medium | [LeetCode 673](https://leetcode.com/problems/number-of-longest-increasing-subsequence/) |\n| Spiral Matrix | Array | Medium | Low | [LeetCode 54](https://leetcode.com/problems/spiral-matrix/) |\n| Container With Most Water | Array, Two Pointers | Medium | Medium | [LeetCode 11](https://leetcode.com/problems/container-with-most-water/) |\n| Find the Duplicate Number | Linked List, Binary Search | Medium | Low | [LeetCode 287](https://leetcode.com/problems/find-the-duplicate-number/) |\n| Largest Number | Sorting | Medium | Medium | [LeetCode 179](https://leetcode.com/problems/largest-number/) |\n| Compare Version Numbers | Two Pointers | Medium | Low | [LeetCode 165](https://leetcode.com/problems/compare-version-numbers/) |\n| Remove Duplicates from Sorted List II | Linked List | Medium | Medium | [LeetCode 82](https://leetcode.com/problems/remove-duplicates-from-sorted-list-ii/) |\n| Next Permutation | Array | Medium | Low | [LeetCode 31](https://leetcode.com/problems/next-permutation/) |\n| Monotone Increasing Digits | Greedy | Medium | Medium | [LeetCode 738](https://leetcode.com/problems/monotone-increasing-digits/) |\n| House Robber II | Dynamic Programming | Medium | Low | [LeetCode 213](https://leetcode.com/problems/house-robber-ii/) |\n| Minimum Window Substring | Hash Table, Sliding Window | Hard | High | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Median of Two Sorted Arrays | Array, Binary Search | Hard | High | [LeetCode 4](https://leetcode.com/problems/median-of-two-sorted-arrays/) |\n| Regular Expression Matching | String, Dynamic Programming | Hard | High | [LeetCode 10](https://leetcode.com/problems/regular-expression-matching/) |\n| Wildcard Matching | String, Dynamic Programming | Hard | High | [LeetCode 44](https://leetcode.com/problems/wildcard-matching/) |\n| Edit Distance | Dynamic Programming | Hard | High | [LeetCode 72](https://leetcode.com/problems/edit-distance/) |\n| Burst Balloons | Dynamic Programming, Interval | Hard | High | [LeetCode 312](https://leetcode.com/problems/burst-balloons/) |\n| Best Time to Buy and Sell Stock with Cooldown | Array, Dynamic Programming | Hard | High | [LeetCode 309](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/) |\n| Best Time to Buy and Sell Stock IV | Array, Dynamic Programming | Hard | High | [LeetCode 188](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/) |\n| Serialize and Deserialize Binary Tree | Tree, Depth-First Search | Hard | High | [LeetCode 297](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) |\n| Expression Add Operators | Backtracking, Dynamic Programming | Hard | High | [LeetCode 282](https://leetcode.com/problems/expression-add-operators/) |\n| Basic Calculator | Stack, Recursion | Hard | High | [LeetCode 224](https://leetcode.com/problems/basic-calculator/) |\n| Alien Dictionary | Graph, Topological Sort | Hard | High | [LeetCode 269](https://leetcode.com/problems/alien-dictionary/) |\n| Course Schedule III | Greedy, Priority Queue | Hard | High | [LeetCode 630](https://leetcode.com/problems/course-schedule-iii/) |\n| Maximum Profit in Job Scheduling | Array, Binary Search, Dynamic Programming | Hard | High | [LeetCode 1235](https://leetcode.com/problems/maximum-profit-in-job-scheduling/) |\n| Sequence Reconstruction | Graph, Topological Sort | Hard | Medium | [LeetCode 444](https://leetcode.com/problems/sequence-reconstruction/) |\n| Sell Diminishing-Valued Colored Balls | Greedy, Priority Queue | Hard | Medium | [LeetCode 1648](https://leetcode.com/problems/sell-diminishing-valued-colored-balls/) |\n| Strong Password Checker | String, Greedy | Hard | Medium | [LeetCode 420](https://leetcode.com/problems/strong-password-checker/) |\n| Sliding Puzzle | Breadth-First Search | Hard | Medium | [LeetCode 773](https://leetcode.com/problems/sliding-puzzle/) |\n| Optimal Account Balancing | Graph, Shortest Path | Hard | Medium | [LeetCode 464](https://leetcode.com/problems/optimal-account-balancing/) |\n| Reverse Nodes in k-Group | Linked List, Recursion | Hard | High | [LeetCode 25](https://leetcode.com/problems/reverse-nodes-in-k-group/) |\n| Longest Valid Parentheses | String, Stack, Dynamic Programming | Hard | Medium | [LeetCode 32](https://leetcode.com/problems/longest-valid-parentheses/) |\n\n### JD.com\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Majority Element | Array, Divide and Conquer | Easy | High | [LeetCode 169](https://leetcode.com/problems/majority-element/) |\n| Search Insert Position | Array, Binary Search | Easy | High | [LeetCode 35](https://leetcode.com/problems/search-insert-position/) |\n| Fibonacci Number | Dynamic Programming | Easy | Medium | [LeetCode 509](https://leetcode.com/problems/fibonacci-number/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Linked List, Recursion | Easy | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Path Sum III | Tree, Depth-First Search | Medium | Medium | [LeetCode 437](https://leetcode.com/problems/path-sum-iii/) |\n| Maximum Product Subarray | Array, Dynamic Programming | Medium | Medium | [LeetCode 152](https://leetcode.com/problems/maximum-product-subarray/) |\n| Sort Array By Parity II | Array, Two Pointers | Medium | Medium | [LeetCode 922](https://leetcode.com/problems/sort-array-by-parity-ii/) |\n| Range Sum Query - Mutable | Fenwick Tree, Segment Tree | Medium | Medium | [LeetCode 307](https://leetcode.com/problems/range-sum-query-mutable/) |\n| Implement Rand10() Using Rand7() | Math, Probability | Medium | Medium | [LeetCode 470](https://leetcode.com/problems/implement-rand10-using-rand7/) |\n| Number of Recent Calls | Design, Sliding Window | Medium | Medium | [LeetCode 933](https://leetcode.com/problems/number-of-recent-calls/) |\n| Design HashMap | Design, Hash Table | Medium | High | [LeetCode 706](https://leetcode.com/problems/design-hashmap/) |\n| Design Linked List | Design, Linked List | Medium | High | [LeetCode 707](https://leetcode.com/problems/design-linked-list/) |\n| Push Dominoes | Simulation, Queue | Medium | Medium | [LeetCode 838](https://leetcode.com/problems/push-dominoes/) |\n| Search in Rotated Sorted Array | Array, Binary Search | Medium | High | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Find Minimum in Rotated Sorted Array | Array, Binary Search | Medium | High | [LeetCode 153](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| 3Sum | Array, Two Pointers | Medium | High | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Kth Largest Element in an Array | Array, Heap, Divide and Conquer | Medium | High | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| Permutations | Array, Backtracking | Medium | High | [LeetCode 46](https://leetcode.com/problems/permutations/) |\n| Linked List Cycle II | Linked List, Two Pointers | Medium | High | [LeetCode 142](https://leetcode.com/problems/linked-list-cycle-ii/) |\n| Sort an Array | Array, Sorting | Medium | High | [LeetCode 912](https://leetcode.com/problems/sort-an-array/) |\n| LRU Cache | Hash Table, Doubly Linked List, Design | Medium | High | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Complex Number Multiplication | Math, String | Medium | Medium | [LeetCode 537](https://leetcode.com/problems/complex-number-multiplication/) |\n| Combinations | Backtracking | Medium | Low | [LeetCode 77](https://leetcode.com/problems/combinations/) |\n| Find First and Last Position of Element in Sorted Array | Array, Binary Search | Medium | Low | [LeetCode 34](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) |\n| Subarray Sum Equals K | Array, Hash Table | Medium | Low | [LeetCode 560](https://leetcode.com/problems/subarray-sum-equals-k/) |\n| Evaluate Reverse Polish Notation | Stack | Medium | Low | [LeetCode 150](https://leetcode.com/problems/evaluate-reverse-polish-notation/) |\n| Binary Tree Right Side View | Tree, Breadth-First Search | Medium | Low | [LeetCode 199](https://leetcode.com/problems/binary-tree-right-side-view/) |\n| Max Area of Island | Depth-First Search, Breadth-First Search | Medium | Low | [LeetCode 695](https://leetcode.com/problems/max-area-of-island/) |\n| Binary Tree Level Order Traversal II | Tree, Breadth-First Search | Medium | Low | [LeetCode 107](https://leetcode.com/problems/binary-tree-level-order-traversal-ii/) |\n| Minimum Window Substring | Hash Table, Sliding Window | Hard | Medium | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Burst Balloons | Dynamic Programming, Interval | Hard | Medium | [LeetCode 312](https://leetcode.com/problems/burst-balloons/) |\n| Optimal Account Balancing | Graph, Shortest Path | Hard | Medium | [LeetCode 464](https://leetcode.com/problems/optimal-account-balancing/) |\n| Strong Password Checker | String, Greedy | Hard | Medium | [LeetCode 420](https://leetcode.com/problems/strong-password-checker/) |\n| Sliding Puzzle | Breadth-First Search | Hard | Medium | [LeetCode 773](https://leetcode.com/problems/sliding-puzzle/) |\n| Sliding Window Maximum | Queue, Sliding Window, Heap | Hard | Low | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Candy | Greedy | Hard | Low | [LeetCode 135](https://leetcode.com/problems/candy/) |\n| First Missing Positive | Array | Hard | Low | [LeetCode 41](https://leetcode.com/problems/first-missing-positive/) |\n\n### Huawei\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Number of 1 Bits | Bit Manipulation | Easy | High | [LeetCode 191](https://leetcode.com/problems/number-of-1-bits/) |\n| Maximum Depth of Binary Tree | Tree, Depth-First Search | Easy | Medium | [LeetCode 104](https://leetcode.com/problems/maximum-depth-of-binary-tree/) |\n| Invert Binary Tree | Tree, Depth-First Search | Easy | Low | [LeetCode 226](https://leetcode.com/problems/invert-binary-tree/) |\n| Path Sum | Tree, Depth-First Search | Easy | Low | [LeetCode 112](https://leetcode.com/problems/path-sum/) |\n| Reverse Integer | Math | Easy | Medium | [LeetCode 7](https://leetcode.com/problems/reverse-integer/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Longest Continuous Increasing Subsequence | Array, Dynamic Programming | Medium | Low | [LeetCode 674](https://leetcode.com/problems/longest-continuous-increasing-subsequence/) |\n| Longest Increasing Subsequence | Array, Dynamic Programming, Binary Search | Medium | High | [LeetCode 300](https://leetcode.com/problems/longest-increasing-subsequence/) |\n| Implement Trie (Prefix Tree) | Design, Data Structure | Medium | Medium | [LeetCode 208](https://leetcode.com/problems/implement-trie-prefix-tree/) |\n| Contains Duplicate III | Array, Sliding Window | Medium | Low | [LeetCode 220](https://leetcode.com/problems/contains-duplicate-iii/) |\n| Flatten Binary Tree to Linked List | Tree, Depth-First Search | Medium | Low | [LeetCode 114](https://leetcode.com/problems/flatten-binary-tree-to-linked-list/) |\n| Symmetric Tree | Tree, Recursion | Medium | Medium | [LeetCode 101](https://leetcode.com/problems/symmetric-tree/) |\n| Binary Tree Level Order Traversal | Tree, Breadth-First Search | Medium | Medium | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Lowest Common Ancestor of a Binary Tree | Tree, Depth-First Search | Medium | Medium | [LeetCode 236](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) |\n| Min Stack | Stack, Design | Medium | High | [LeetCode 155](https://leetcode.com/problems/min-stack/) |\n| Sliding Window Maximum | Queue, Sliding Window | Medium | High | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Daily Temperatures | Stack, Monotonic Stack | Medium | Medium | [LeetCode 739](https://leetcode.com/problems/daily-temperatures/) |\n| Brick Wall | Array, Hash Table | Medium | Low | [LeetCode 554](https://leetcode.com/problems/brick-wall/) |\n| 3Sum | Array, Two Pointers | Medium | High | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Permutations | Array, Backtracking | Medium | Medium | [LeetCode 46](https://leetcode.com/problems/permutations/) |\n| Number of Islands | Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Merge Intervals | Array, Sorting | Medium | Medium | [LeetCode 56](https://leetcode.com/problems/merge-intervals/) |\n| Coin Change | Dynamic Programming | Medium | Medium | [LeetCode 322](https://leetcode.com/problems/coin-change/) |\n| Longest Palindromic Substring | String, Dynamic Programming | Medium | High | [LeetCode 5](https://leetcode.com/problems/longest-palindromic-substring/) |\n| Remove Duplicate Letters | String, Monotonic Stack | Medium | Low | [LeetCode 316](https://leetcode.com/problems/remove-duplicate-letters/) |\n| Basic Calculator II | Stack, Math | Medium | Low | [LeetCode 227](https://leetcode.com/problems/basic-calculator-ii/) |\n| Decode String | Stack, String | Medium | Medium | [LeetCode 394](https://leetcode.com/problems/decode-string/) |\n| Restore IP Addresses | String, Backtracking | Medium | Low | [LeetCode 93](https://leetcode.com/problems/restore-ip-addresses/) |\n| Reverse Nodes in k-Group | Linked List, Recursion | Hard | Medium | [LeetCode 25](https://leetcode.com/problems/reverse-nodes-in-k-group/) |\n| Merge k Sorted Lists | Linked List, Heap, Divide and Conquer | Hard | Medium | [LeetCode 23](https://leetcode.com/problems/merge-k-sorted-lists/) |\n| Regular Expression Matching | String, Dynamic Programming | Hard | Low | [LeetCode 10](https://leetcode.com/problems/regular-expression-matching/) |\n| Minimum Window Substring | Hash Table, Sliding Window | Hard | Low | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Median of Two Sorted Arrays | Array, Binary Search | Hard | Medium | [LeetCode 4](https://leetcode.com/problems/median-of-two-sorted-arrays/) |\n| Largest Rectangle in Histogram | Stack, Array, Monotonic Stack | Hard | Low | [LeetCode 84](https://leetcode.com/problems/largest-rectangle-in-histogram/) |\n| Edit Distance | String, Dynamic Programming | Hard | Medium | [LeetCode 72](https://leetcode.com/problems/edit-distance/) |\n| Word Ladder | Graph, Breadth-First Search | Hard | Low | [LeetCode 127](https://leetcode.com/problems/word-ladder/) |\n| The Skyline Problem | Fenwick Tree, Segment Tree, Sweep Line | Hard | Low | [LeetCode 218](https://leetcode.com/problems/the-skyline-problem/) |\n| Burst Balloons | Dynamic Programming, Interval | Hard | Low | [LeetCode 312](https://leetcode.com/problems/burst-balloons/) |\n| Optimal Account Balancing | Graph, Dynamic Programming, State Compression | Hard | Low | [LeetCode 464](https://leetcode.com/problems/optimal-account-balancing/) |\n\n### Xiaomi\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Kth Largest Element in a Stream | Heap, Design | Easy | High | [LeetCode 703](https://leetcode.com/problems/kth-largest-element-in-a-stream/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Merge Two Sorted Lists | Linked List, Recursion | Easy | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Maximum Subarray | Array, Divide and Conquer, Dynamic Programming | Easy | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Merge Sorted Array | Array, Two Pointers | Easy | High | [LeetCode 88](https://leetcode.com/problems/merge-sorted-array/) |\n| Add Two Numbers | Linked List, Math | Medium | High | [LeetCode 2](https://leetcode.com/problems/add-two-numbers/) |\n| Sort Colors | Array, Two Pointers, Sorting | Medium | High | [LeetCode 75](https://leetcode.com/problems/sort-colors/) |\n| Decode String | Stack, String | Medium | High | [LeetCode 394](https://leetcode.com/problems/decode-string/) |\n| Number of Islands | Depth-First Search, Breadth-First Search, Union Find | Medium | High | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Longest Palindromic Substring | String, Dynamic Programming | Medium | High | [LeetCode 5](https://leetcode.com/problems/longest-palindromic-substring/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Binary Tree Level Order Traversal | Tree, Breadth-First Search | Medium | High | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Kth Largest Element in an Array | Array, Heap, Divide and Conquer | Medium | High | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| Reorder List | Linked List, Stack | Medium | Medium | [LeetCode 143](https://leetcode.com/problems/reorder-list/) |\n| 3Sum | Array, Two Pointers | Medium | High | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Implement Queue using Stacks | Stack, Design | Medium | Medium | [LeetCode 232](https://leetcode.com/problems/implement-queue-using-stacks/) |\n| Implement Stack using Queues | Design, Queue | Medium | Medium | [LeetCode 225](https://leetcode.com/problems/implement-stack-using-queues/) |\n| Remove Nth Node From End of List | Linked List, Two Pointers | Medium | High | [LeetCode 19](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) |\n| Search in Rotated Sorted Array | Array, Binary Search | Medium | Medium | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Longest Common Subsequence | Array, Dynamic Programming | Medium | Medium | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n| Edit Distance | String, Dynamic Programming | Hard | Medium | [LeetCode 72](https://leetcode.com/problems/edit-distance/) |\n| Longest Valid Parentheses | String, Stack, Dynamic Programming | Hard | Medium | [LeetCode 32](https://leetcode.com/problems/longest-valid-parentheses/) |\n| Find Median from Data Stream | Design, Heap | Hard | Medium | [LeetCode 295](https://leetcode.com/problems/find-median-from-data-stream/) |\n| Median of Two Sorted Arrays | Array, Binary Search | Hard | Medium | [LeetCode 4](https://leetcode.com/problems/median-of-two-sorted-arrays/) |\n| Largest Rectangle in Histogram | Stack, Array | Hard | Medium | [LeetCode 84](https://leetcode.com/problems/largest-rectangle-in-histogram/) |\n| The Skyline Problem | Fenwick Tree, Segment Tree, Sweep Line | Hard | Low | [LeetCode 218](https://leetcode.com/problems/the-skyline-problem/) |\n| Maximal Rectangle | Stack, Array, Dynamic Programming | Hard | Low | [LeetCode 85](https://leetcode.com/problems/maximal-rectangle/) |\n\n### Microsoft\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Product of Array Except Self | Medium | Array, Prefix Sum | Medium | [LeetCode 238](https://leetcode.com/problems/product-of-array-except-self/) |\n| Container With Most Water | Medium | Array, Two Pointers | Medium | [LeetCode 11](https://leetcode.com/problems/container-with-most-water/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| Rotate Array | Medium | Array, Math | Low | [LeetCode 189](https://leetcode.com/problems/rotate-array/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Low | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Low | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Low | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Longest Palindromic Substring | Medium | String, Dynamic Programming | Low | [LeetCode 5](https://leetcode.com/problems/longest-palindromic-substring/) |\n| Combination Sum | Medium | Backtracking, Array | Low | [LeetCode 39](https://leetcode.com/problems/combination-sum/) |\n| Permutations | Medium | Backtracking, Array | Low | [LeetCode 46](https://leetcode.com/problems/permutations/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Serialize and Deserialize Binary Tree | Hard | Tree, String | Low | [LeetCode 297](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) |\n\n### Didi\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Design HashMap | Easy | Hash Table, Design | Medium | [LeetCode 706](https://leetcode.com/problems/design-hashmap/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| 3Sum | Medium | Array, Two Pointers | Medium | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Remove Nth Node From End of List | Medium | Linked List, Two Pointers | Medium | [LeetCode 19](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Sliding Window Maximum | Medium | Array, Sliding Window | High | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| Combination Sum | Medium | Backtracking, Array | Low | [LeetCode 39](https://leetcode.com/problems/combination-sum/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Longest Common Subsequence | Medium | Dynamic Programming, String | Low | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n| Reservoir Sampling | Medium | Math, Rejection Sampling | Low | [LeetCode 382](https://leetcode.com/problems/linked-list-random-node/) |\n| Serialize and Deserialize Binary Tree | Hard | Tree, String | Low | [LeetCode 297](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) |\n\n### Ctrip\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Intersection of Two Linked Lists | Easy | Linked List, Two Pointers | Low | [LeetCode 160](https://leetcode.com/problems/intersection-of-two-linked-lists/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Sliding Window Maximum | Medium | Array, Sliding Window | High | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| Cheapest Flights Within K Stops | Medium | Graph, Dynamic Programming | Medium | [LeetCode 787](https://leetcode.com/problems/cheapest-flights-within-k-stops/) |\n| Next Permutation | Medium | Array, Two Pointers | Low | [LeetCode 31](https://leetcode.com/problems/next-permutation/) |\n| Reconstruct Itinerary | Hard | Graph, Depth-First Search | Medium | [LeetCode 332](https://leetcode.com/problems/reconstruct-itinerary/) |\n| Bus Routes | Breadth-First Search, Array | Medium | Low | [LeetCode 815](https://leetcode.com/problems/bus-routes/) |\n| 3Sum | Medium | Array, Two Pointers | Low | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Remove Nth Node From End of List | Medium | Linked List, Two Pointers | Low | [LeetCode 19](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Longest Common Subsequence | Medium | Dynamic Programming, String | Low | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n| Combination Sum | Medium | Backtracking, Array | Low | [LeetCode 39](https://leetcode.com/problems/combination-sum/) |\n\n### Pinduoduo\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Majority Element | Easy | Array, Bit Manipulation | Low | [LeetCode 169](https://leetcode.com/problems/majority-element/) |\n| Trapping Rain Water | Hard | Array, Two Pointers | High | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| Minimum Window Substring | Hard | Hash Table, Sliding Window | High | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Sliding Window Maximum | Medium | Array, Sliding Window | High | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| 3Sum | Medium | Array, Two Pointers | Low | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| House Robber | Medium | Dynamic Programming, Array | Low | [LeetCode 198](https://leetcode.com/problems/house-robber/) |\n| Partition Equal Subset Sum | Medium | Dynamic Programming, Array | Low | [LeetCode 416](https://leetcode.com/problems/partition-equal-subset-sum/) |\n| Construct Binary Tree from Preorder and Inorder Traversal | Medium | Tree, Depth-First Search | Low | [LeetCode 105](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/) |\n| Reorder List | Medium | Linked List, Two Pointers | Low | [LeetCode 143](https://leetcode.com/problems/reorder-list/) |\n| Sort List | Medium | Linked List, Two Pointers | Low | [LeetCode 148](https://leetcode.com/problems/sort-list/) |\n| Binary Tree Level Order Traversal | Medium | Tree, Breadth-First Search | Low | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Compare Version Numbers | Medium | String, Two Pointers | Low | [LeetCode 165](https://leetcode.com/problems/compare-version-numbers/) |\n| Min Stack | Medium | Stack, Design | Low | [LeetCode 155](https://leetcode.com/problems/min-stack/) |\n| Largest Rectangle in Histogram | Hard | Array, Stack | Low | [LeetCode 84](https://leetcode.com/problems/largest-rectangle-in-histogram/) |\n| Merge k Sorted Lists | Hard | Linked List, Heap | Low | [LeetCode 23](https://leetcode.com/problems/merge-k-sorted-lists/) |\n| Find Median from Data Stream | Hard | Array, Binary Search | Low | [LeetCode 295](https://leetcode.com/problems/find-median-from-data-stream/) |\n| Sliding Window Median | Hard | Heap, Design | Low | [LeetCode 295](https://leetcode.com/problems/sliding-window-median/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Longest Common Subsequence | Medium | Dynamic Programming, String | Low | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n\n### Xiaohongshu\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| Sum Root to Leaf Numbers | Medium | Tree, Depth-First Search | Medium | [LeetCode 129](https://leetcode.com/problems/sum-root-to-leaf-numbers/) |\n| Surrounded Regions | Medium | Depth-First Search, Breadth-First Search | Low | [LeetCode 130](https://leetcode.com/problems/surrounded-regions/) |\n| Binary Tree Level Order Traversal | Medium | Tree, Breadth-First Search | Low | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Longest Increasing Subsequence | Medium | Dynamic Programming, Array | High | [LeetCode 300](https://leetcode.com/problems/longest-increasing-subsequence/) |\n| Interleaving String | Medium | Dynamic Programming, String | Medium | [LeetCode 97](https://leetcode.com/problems/interleaving-string/) |\n| Trapping Rain Water | Hard | Array, Two Pointers | High | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| Longest Palindromic Substring | Medium | String, Dynamic Programming | Low | [LeetCode 5](https://leetcode.com/problems/longest-palindromic-substring/) |\n| 3Sum | Medium | Array, Two Pointers | Low | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Longest Common Subsequence | Medium | Dynamic Programming, String | Low | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n| Combination Sum | Medium | Backtracking, Array | Low | [LeetCode 39](https://leetcode.com/problems/combination-sum/) |\n\n### vivo\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| Binary Tree Level Order Traversal | Medium | Tree, Breadth-First Search | High | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Path Sum | Easy | Tree, Depth-First Search | Medium | [LeetCode 112](https://leetcode.com/problems/path-sum/) |\n| Invert Binary Tree | Easy | Tree, Recursion | Low | [LeetCode 226](https://leetcode.com/problems/invert-binary-tree/) |\n| Android Unlock Patterns | Medium | Depth-First Search, Backtracking | Low | [LeetCode 351](https://leetcode.com/problems/android-unlock-patterns/) |\n| Trapping Rain Water | Hard | Array, Two Pointers | Low | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| 3Sum | Medium | Array, Two Pointers | Low | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Longest Common Subsequence | Medium | Dynamic Programming, String | Low | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n| Combination Sum | Medium | Backtracking, Array | Low | [LeetCode 39](https://leetcode.com/problems/combination-sum/) |\n\n### OPPO\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Reverse Linked List | Easy | Linked List, Recursion | Medium | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Container With Most Water | Medium | Array, Two Pointers | Medium | [LeetCode 11](https://leetcode.com/problems/container-with-most-water/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| Minimum Window Substring | Hard | Hash Table, Sliding Window | Low | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Longest Valid Parentheses | Medium | Stack, String | Low | [LeetCode 32](https://leetcode.com/problems/longest-valid-parentheses/) |\n| Substring with Concatenation of All Words | Medium | Hash Table, Sliding Window | Low | [LeetCode 30](https://leetcode.com/problems/substring-with-concatenation-of-all-words/) |\n| Binary Tree Maximum Path Sum | Hard | Tree, Depth-First Search | Low | [LeetCode 124](https://leetcode.com/problems/binary-tree-maximum-path-sum/) |\n| Trapping Rain Water | Hard | Array, Two Pointers | Low | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| 3Sum | Medium | Array, Two Pointers | Low | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Group Anagrams | Medium | String, Hash Table | Low | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Search in Rotated Sorted Array | Medium | Binary Search, Array | Low | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Jump Game | Medium | Greedy, Array | Low | [LeetCode 55](https://leetcode.com/problems/jump-game/) |\n| Word Break | Medium | Dynamic Programming, String | Low | [LeetCode 139](https://leetcode.com/problems/word-break/) |\n| Longest Common Subsequence | Medium | Dynamic Programming, String | Low | [LeetCode 1143](https://leetcode.com/problems/longest-common-subsequence/) |\n| Combination Sum | Medium | Backtracking, Array | Low | [LeetCode 39](https://leetcode.com/problems/combination-sum/) |\n\n### Ant Group\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| House Robber | Medium | Dynamic Programming, Array | High | [LeetCode 198](https://leetcode.com/problems/house-robber/) |\n| Partition Equal Subset Sum | Medium | Dynamic Programming, Array | Medium | [LeetCode 416](https://leetcode.com/problems/partition-equal-subset-sum/) |\n| Task Scheduler | Medium | Greedy, Array | Medium | [LeetCode 621](https://leetcode.com/problems/task-scheduler/) |\n\n### iFlytek\n| Problem Name | Difficulty | Tags | Frequency | Problem Link |\n|--------------|------------|------|-----------|--------------|\n| Two Sum | Easy | Array, Hash Table | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Easy | Stack, String | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Merge Two Sorted Lists | Easy | Linked List, Recursion | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Climbing Stairs | Easy | Dynamic Programming, Array | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Valid Palindrome | Easy | String, Two Pointers | Medium | [LeetCode 125](https://leetcode.com/problems/valid-palindrome/) |\n| Maximum Subarray | Medium | Array, Dynamic Programming | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Best Time to Buy and Sell Stock | Medium | Array, Dynamic Programming | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Longest Substring Without Repeating Characters | Medium | String, Sliding Window | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Kth Largest Element in an Array | Medium | Array, Heap | Medium | [LeetCode 215](https://leetcode.com/problems/kth-largest-element-in-an-array/) |\n| LRU Cache | Medium | Hash Table, Doubly Linked List | Medium | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Course Schedule | Medium | Graph, Depth-First Search | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Number of Islands | Medium | Depth-First Search, Breadth-First Search | Medium | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Minimum Path Sum | Medium | Dynamic Programming, Matrix | Medium | [LeetCode 64](https://leetcode.com/problems/minimum-path-sum/) |\n| Longest Increasing Subsequence | Medium | Dynamic Programming, Array | High | [LeetCode 300](https://leetcode.com/problems/longest-increasing-subsequence/) |\n| Interleaving String | Medium | Dynamic Programming, String | Medium | [LeetCode 97](https://leetcode.com/problems/interleaving-string/) |\n| Edit Distance | Medium | Dynamic Programming, String | Medium | [LeetCode 72](https://leetcode.com/problems/edit-distance/) |\n\n### Meta\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Two Sum | Array, Hash Table | Easy | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Linked List Cycle | Linked List, Two Pointers | Easy | High | [LeetCode 141](https://leetcode.com/problems/linked-list-cycle/) |\n| Maximum Subarray | Array, Divide and Conquer, Dynamic Programming | Easy | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Climbing Stairs | Dynamic Programming, Memoization | Easy | Medium | [LeetCode 70](https://leetcode.com/problems/climbing-stairs/) |\n| Number of Islands | Depth-First Search, Breadth-First Search, Union Find | Medium | High | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Clone Graph | Depth-First Search, Breadth-First Search, Graph | Medium | High | [LeetCode 133](https://leetcode.com/problems/clone-graph/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Merge Intervals | Array, Sorting | Medium | High | [LeetCode 56](https://leetcode.com/problems/merge-intervals/) |\n| Validate Binary Search Tree | Tree, Depth-First Search | Medium | High | [LeetCode 98](https://leetcode.com/problems/validate-binary-search-tree/) |\n| Lowest Common Ancestor of a Binary Tree | Tree, Depth-First Search, Binary Tree | Medium | High | [LeetCode 236](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) |\n| Course Schedule | Depth-First Search, Breadth-First Search, Graph | Medium | High | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Group Anagrams | Hash Table, String, Sorting | Medium | Medium | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Sliding Window Maximum | Array, Sliding Window, Queue | Medium | Medium | [LeetCode 239](https://leetcode.com/problems/sliding-window-maximum/) |\n| Pacific Atlantic Waterflow | Depth-First Search, Breadth-First Search, Array | Medium | Medium | [LeetCode 417](https://leetcode.com/problems/pacific-atlantic-waterflow/) |\n| Task Scheduler | Array, Greedy, Sorting | Medium | Medium | [LeetCode 621](https://leetcode.com/problems/task-scheduler/) |\n| Serialize and Deserialize Binary Tree | Tree, Depth-First Search, Breadth-First Search | Medium | Medium | [LeetCode 297](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) |\n| Minimum Window Substring | Hash Table, String, Sliding Window | Hard | Medium | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Word Ladder | Breadth-First Search, Hash Table, String | Hard | Medium | [LeetCode 127](https://leetcode.com/problems/word-ladder/) |\n| Sliding Window Median | Design, Hash Table, Sliding Window | Hard | Medium | [LeetCode 480](https://leetcode.com/problems/sliding-window-median/) |\n| Verifying an Alien Dictionary | Hash Table, String, Greedy | Hard | Low | [LeetCode 953](https://leetcode.com/problems/verifying-an-alien-dictionary/) |\n| Find Longest Awesome Substring | Greedy, String, Dynamic Programming | Hard | Low | [LeetCode 1542](https://leetcode.com/problems/find-longest-awesome-substring/) |\n| Build Array Where You Can Find The Maximum Exactly K Comparisons | Dynamic Programming, String | Hard | Low | [LeetCode 1420](https://leetcode.com/problems/build-array-where-you-can-find-the-maximum-exactly-k-comparisons/) |\n\n### Google\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Two Sum | Array, Hash Table | Easy | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Valid Parentheses | Stack, String | Easy | High | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Linked List Cycle | Linked List, Two Pointers | Easy | High | [LeetCode 141](https://leetcode.com/problems/linked-list-cycle/) |\n| Maximum Subarray | Array, Divide and Conquer, Dynamic Programming | Easy | Medium | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Happy Number | Hash Table, Math, Two Pointers | Easy | Medium | [LeetCode 202](https://leetcode.com/problems/happy-number/) |\n| Number of Islands | Depth-First Search, Breadth-First Search, Union Find | Medium | High | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| Lowest Common Ancestor of a Binary Tree | Tree, Depth-First Search, Binary Tree | Medium | High | [LeetCode 236](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/) |\n| Merge Intervals | Array, Sorting | Medium | High | [LeetCode 56](https://leetcode.com/problems/merge-intervals/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | High | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| 3Sum | Array, Two Pointers, Sorting | Medium | High | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Validate Binary Search Tree | Tree, Depth-First Search | Medium | High | [LeetCode 98](https://leetcode.com/problems/validate-binary-search-tree/) |\n| Decode String | Stack, Recursion, String | Medium | Medium | [LeetCode 394](https://leetcode.com/problems/decode-string/) |\n| Unique Paths | Array, Dynamic Programming | Medium | Medium | [LeetCode 62](https://leetcode.com/problems/unique-paths/) |\n| Meeting Rooms II | Heap, Sorting, Interval | Medium | Medium | [LeetCode 253](https://leetcode.com/problems/meeting-rooms-ii/) |\n| Evaluate Reverse Polish Notation | Stack, Array, Math | Medium | Medium | [LeetCode 150](https://leetcode.com/problems/evaluate-reverse-polish-notation/) |\n| Course Schedule | Depth-First Search, Breadth-First Search, Graph | Medium | Medium | [LeetCode 207](https://leetcode.com/problems/course-schedule/) |\n| Subsets | Bit Manipulation, Array, Backtracking | Medium | Medium | [LeetCode 78](https://leetcode.com/problems/subsets/) |\n| Search in Rotated Sorted Array | Array, Binary Search | Medium | Medium | [LeetCode 33](https://leetcode.com/problems/search-in-rotated-sorted-array/) |\n| Longest Palindromic Substring | Hash Table, String, Dynamic Programming | Medium | Medium | [LeetCode 5](https://leetcode.com/problems/longest-palindromic-substring/) |\n| Word Search | Array, Backtracking, Matrix | Medium | Medium | [LeetCode 79](https://leetcode.com/problems/word-search/) |\n| Meeting Rooms | Sorting, Heap, Greedy | Medium | Low | [LeetCode 252](https://leetcode.com/problems/meeting-rooms/) |\n| Minimum Time Difference | Heap, Sorting | Medium | Low | [LeetCode 539](https://leetcode.com/problems/minimum-time-difference/) |\n| Trapping Rain Water | Stack, Array, Two Pointers | Hard | Medium | [LeetCode 42](https://leetcode.com/problems/trapping-rain-water/) |\n| Minimum Window Substring | Hash Table, String, Sliding Window | Hard | Medium | [LeetCode 76](https://leetcode.com/problems/minimum-window-substring/) |\n| Median of Two Sorted Arrays | Array, Binary Search | Hard | Low | [LeetCode 4](https://leetcode.com/problems/median-of-two-sorted-arrays/) |\n| Word Ladder | Breadth-First Search, Hash Table, String | Hard | Low | [LeetCode 127](https://leetcode.com/problems/word-ladder/) |\n| Regular Expression Matching | String, Dynamic Programming, Backtracking | Hard | Low | [LeetCode 10](https://leetcode.com/problems/regular-expression-matching/) |\n### Amazon\n| Problem Name | Tags | Difficulty | Frequency | Problem Link |\n|--------------|------|------------|-----------|--------------|\n| Two Sum | Array, Hash Table | Easy | High | [LeetCode 1](https://leetcode.com/problems/two-sum/) |\n| Merge Two Sorted Lists | Linked List, Recursion | Easy | High | [LeetCode 21](https://leetcode.com/problems/merge-two-sorted-lists/) |\n| Reverse Linked List | Linked List, Recursion | Easy | High | [LeetCode 206](https://leetcode.com/problems/reverse-linked-list/) |\n| Best Time to Buy and Sell Stock | Array, Dynamic Programming | Easy | High | [LeetCode 121](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/) |\n| Longest Palindrome | String | Easy | High | [LeetCode 409](https://leetcode.com/problems/longest-palindrome/) |\n| Linked List Cycle | Linked List, Two Pointers | Easy | High | [LeetCode 141](https://leetcode.com/problems/linked-list-cycle/) |\n| Palindrome Linked List | Linked List, Two Pointers | Easy | High | [LeetCode 234](https://leetcode.com/problems/palindrome-linked-list/) |\n| Intersection of Two Linked Lists | Linked List, Two Pointers | Easy | High | [LeetCode 160](https://leetcode.com/problems/intersection-of-two-linked-lists/) |\n| Valid Parentheses | Stack, String | Easy | Medium | [LeetCode 20](https://leetcode.com/problems/valid-parentheses/) |\n| Valid Anagram | Hash Table, String | Easy | Medium | [LeetCode 242](https://leetcode.com/problems/valid-anagram/) |\n| Number of Islands | Depth-First Search, Breadth-First Search, Union Find | Medium | High | [LeetCode 200](https://leetcode.com/problems/number-of-islands/) |\n| LRU Cache | Design, Hash Table, Linked List | Medium | High | [LeetCode 146](https://leetcode.com/problems/lru-cache/) |\n| Maximum Subarray | Array, Divide and Conquer, Dynamic Programming | Medium | High | [LeetCode 53](https://leetcode.com/problems/maximum-subarray/) |\n| Product of Array Except Self | Array, Prefix Sum | Medium | High | [LeetCode 238](https://leetcode.com/problems/product-of-array-except-self/) |\n| Invert Binary Tree | Tree, Depth-First Search, Breadth-First Search | Medium | High | [LeetCode 226](https://leetcode.com/problems/invert-binary-tree/) |\n| Binary Tree Inorder Traversal | Stack, Tree, Depth-First Search | Medium | High | [LeetCode 94](https://leetcode.com/problems/binary-tree-inorder-traversal/) |\n| Set Matrix Zeroes | Array, Hash Table, Matrix | Medium | High | [LeetCode 73](https://leetcode.com/problems/set-matrix-zeroes/) |\n| Longest Substring Without Repeating Characters | Hash Table, String, Sliding Window | Medium | Medium | [LeetCode 3](https://leetcode.com/problems/longest-substring-without-repeating-characters/) |\n| Longest Palindromic Substring | Hash Table, String, Dynamic Programming | Medium | Medium | [LeetCode 5](https://leetcode.com/problems/longest-palindromic-substring/) |\n| 3Sum | Array, Two Pointers, Sorting | Medium | Medium | [LeetCode 15](https://leetcode.com/problems/3sum/) |\n| Group Anagrams | Hash Table, String, Sorting | Medium | Medium | [LeetCode 49](https://leetcode.com/problems/group-anagrams/) |\n| Merge Intervals | Array, Sorting | Medium | Medium | [LeetCode 56](https://leetcode.com/problems/merge-intervals/) |\n| Top K Frequent Elements | Array, Hash Table, Heap | Medium | Medium | [LeetCode 347](https://leetcode.com/problems/top-k-frequent-elements/) |\n| Subarray Sum Equals K | Array, Hash Table, Prefix Sum | Medium | Medium | [LeetCode 560](https://leetcode.com/problems/subarray-sum-equals-k/) |\n| Validate Binary Search Tree | Tree, Depth-First Search | Medium | Medium | [LeetCode 98](https://leetcode.com/problems/validate-binary-search-tree/) |\n| Binary Tree Level Order Traversal | Tree, Breadth-First Search, Binary Tree | Medium | Medium | [LeetCode 102](https://leetcode.com/problems/binary-tree-level-order-traversal/) |\n| Lowest Common Ancestor of a Binary Tree | Tree, Depth-First Search, Binary Tree | Medium | Medi","projects_url":"https://awesome.ecosyste.ms/api/v1/lists/0voice%2Fawesome-interview-algorithms/projects"}