---
title: "340. Longest Substring with At Most K Distinct Character"
url: "https://laigary.com/interview/coding/340-longest-substring-with-at-most-k-distinct-character"
type: "note"
section: "coding"
date: "2023-01-29"
updated: "2024-03-09"
tags: ["Sliding Window"]
---

# 340. Longest Substring with At Most K Distinct Character

[340\. Longest Substring with At Most K Distinct Character](https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/)

[159\. Longest Substring with At Most Two Distinct Characters](/interview/coding/159-longest-substring-with-at-most-two-distinct-characters) 的泛化版。

```python
class Solution:
    def lengthOfLongestSubstringKDistinct(self, s: str, k: int) -> int:
        fast = 0
        slow = 0
        memo = defaultdict(int)
        res = 0
        while fast < len(s):
            char = s[fast]
            fast += 1

            memo[char] += 1

            while len(memo) > k:
                d = s[slow]
                slow += 1
                memo[d] -= 1
                if memo[d] == 0:
                    del memo[d]
            res = max(res, fast - slow)
        return res

```