https://github.com/ziy1-tan/lc-solutions

⏳ LeetCode for job
https://github.com/ziy1-tan/lc-solutions

leetcode-cpp leetcode-solutions python

Last synced: 23 days ago
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⏳ LeetCode for job

• Host: GitHub
• URL: https://github.com/ziy1-tan/lc-solutions
• Owner: Ziy1-Tan
• Created: 2022-02-09T08:22:06.000Z (over 2 years ago)
• Default Branch: master
• Last Pushed: 2024-03-16T05:50:21.000Z (8 months ago)
• Last Synced: 2024-03-16T06:38:29.662Z (8 months ago)
• Topics: leetcode-cpp, leetcode-solutions, python
• Language: C++
• Homepage:
• Size: 3.84 MB
• Stars: 5
• Watchers: 1
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

Awesome Lists containing this project

README

        
# 刷题顺序

1. [CodeTop](https://codetop.cc/home) 高频题

2. [LeetCode](https://leetcode.cn/studyplan/top-100-liked/) Hot100

# 题单

## 链表

![linkedlist](./images/2.png)

## 树

![tree](./images/3.png)

## DFS / BFS

![dfs](./images/4.png)

## DP

![dp](./images/5.png)

## 小专题

![other](./images/6.png)

![other](./images/7.png)

# 复习频率

![freq](./images/1.png)

# Tips

## 二叉树的前中后序遍历（144、94、145）

注意结果打印位置即可

- 前序

```c++

while (root || !stack.empty()) {

    while (root)

    {

        res.push_back(root->val);

        stack.push(root);

        root = root->left;

    }

    root = stack.top();

    stack.pop();

    root = root->right;

}

```

- 中序

```c++

while (root || !stack.empty()) {

    while (root) {

        stack.push(root);

        root = root->left;

    }

    root = stack.top();

    stack.pop();

    res.push_back(root->val);

    root = root->right;

}

```

- 后序

```c++

while (root || !stack.empty()) {

    while (root) {

        res.push_back(root->val);

        stack.push(root);

        root = root->right;

    }

    root = stack.top();

    stack.pop();

    root = root->left;

}

reverse(res.begin(), res.end());

```

## 组合问题

### 下标记录回溯深度的场景

- 以下标 i 来表示从 i 开始选取避免重复

- 对结果顺序无要求：[1,2] 和 [2,1] 算是同一种结果

- 39.组合综合、40.组合总和II、216.组合总和III等

```c++

for (int i = idx; i < candidates.size(); i++) {

    if (rest - candidates[i] >= 0) {

        path.push_back(candidates[i]);

        dfs(candidates, rest - candidates[i], i);

        path.pop_back();

    }

}

```

### used 数组使用的场景

- 用`used[i]`来表示已经选过避免重复

- 对结果顺序有要求：[1,2] 和 [2,1] 算是不同结果

- 46.全排列、47.全排列II、剑指Offer38.字符串的排列

```c++

for (int i = 0; i < nums.size(); i++) {

    if (used[i])

        continue;

    used[i] = 1;

    path.push_back(nums[i]);

    dfs(nums);

    path.pop_back();

    used[i] = 0;

}

```

### 需要排序剪枝的场景

- 排序后判断`nums[i]==nums[i-1]`跳过选择避免重复

- 数组中有重复元素：数组 [1,2,2,3]，选择 0、1 元素和选择 0、2 元素产生的结果相同

- 40.组合总和II、47.全排列II、剑指Offer38.字符串的排列、90.子集II

```c++

for (int i = idx; i < candidates.size(); i++) {

    // 同层不重复，同路径可以重复

    if (i > idx && candidates[i] == candidates[i - 1])

        continue;

    ...

}

```