https://github.com/emahtab/longest-substring-with-at-most-k-distinct-characters
Longest Substring with At Most K Distinct Characters
https://github.com/emahtab/longest-substring-with-at-most-k-distinct-characters
leetcode sliding-window substring
Last synced: 3 months ago
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Longest Substring with At Most K Distinct Characters
- Host: GitHub
- URL: https://github.com/emahtab/longest-substring-with-at-most-k-distinct-characters
- Owner: eMahtab
- Created: 2024-10-08T14:10:47.000Z (about 1 year ago)
- Default Branch: main
- Last Pushed: 2025-01-18T15:51:22.000Z (9 months ago)
- Last Synced: 2025-03-18T23:20:33.032Z (7 months ago)
- Topics: leetcode, sliding-window, substring
- Homepage:
- Size: 4.88 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# Longest Substring with At Most K Distinct Characters
https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters
Given a string s and an integer k, return the length of the longest substring of s that contains at most k distinct characters.
```java
Example 1:
Input: s = "eceba", k = 2
Output: 3
Explanation: The substring is "ece" with length 3.
Example 2:
Input: s = "aa", k = 1
Output: 2
Explanation: The substring is "aa" with length 2.
```
## Constraints:
1. 1 <= s.length <= 5 * 10^4
2. 0 <= k <= 50
## Implementation : Sliding Window
```java
class Solution {
public int lengthOfLongestSubstringKDistinct(String s, int k) {
int n = s.length();
if (n <= k) return n;
int left = 0, right = 0;
HashMap hashmap = new HashMap();
int max_len = k;
while (right < n) {
hashmap.put(s.charAt(right), right);
if (hashmap.size() > k) {
int del_idx = Collections.min(hashmap.values());
hashmap.remove(s.charAt(del_idx));
left = del_idx + 1;
}
max_len = Math.max(max_len, right - left + 1);
right++;
}
return max_len;
}
}
```
## Note : Taking k=2 as example
In above implementation, when updating the left pointer, **make sure you are deleting the least recent character.**
It would be wrong to delete the recent occurrence of character pointed by left pointer, character at left may not be the least recent one.
e.g. {1,2,1,2,1,3,3,3,3,3}, **when seeing value 3, we should delete value 2 (because that was the least recent from 3 values in the map), and we should move the left pointer to point to 1.**
So answer in this case would be 6.
## References :
https://github.com/eMahtab/longest-substring-with-at-most-two-distinct-characters