L 340.Longest Substring with At Most K Distinct Characters ---H

 Given a string, find the length of the longest substring T that contains at most k distinct characters.

Example 1:

Input: s = "eceba", k = 2
Output: 3
Explanation: T is "ece" which its length is 3.

Example 2:

Input: s = "aa", k = 1
Output: 2
Explanation: T is "aa" which its length is 2.

A:

就是用 HashMap 开计算 number of different characters.

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class Solution { public: int lengthOfLongestSubstringKDistinct(string s, int k) { unordered_map<char, int> M; int start = 0; int res = 0; for(int end = 0;end<s.length();end++){ char ch = s[end]; M[ch]++; while(M.size() > k){ char delChar = s[start++]; M[delChar]--; if(M[delChar] ==0){ M.erase(delChar); } } res = max(res, end-start+1); } return res; } };