340. Longest Substring with At Most K Distinct Characters

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

For example, Given s = “eceba” and k = 2,

T is "ece" which its length is 3

 

class Solution {
public:
    int lengthOfLongestSubstringKDistinct(string s, int k) {
        if(s.empty()||k==0) return 0;
        unordered_map<char,int> mp;
        int left = 0,right = 0;
        int disticnt = 0; 
        int res = INT_MIN;
        while(right<s.size())
        {
            if(mp[s[right]]==0) disticnt++;
            mp[s[right]]++;
            while(disticnt>k)
            {
                mp[s[left]]--;
                if(mp[s[left]]==0) disticnt--;
                left++;
            }
            res = max(res,right-left+1);
            right++;
        }
        return res;
    }
};