[LeetCode] Longest Substring with At Most Two Distinct Characters

Longest Substring with At Most Two Distinct Characters 

Given a string, find the length of the longest substring T that contains at most 2 distinct characters.

For example, Given s = “eceba”,

T is "ece" which its length is 3.

滑动窗口。

class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        int res = 0, start = 0, end = 0;
        vector<int> mp(256, 0);
        int cnt = 0;
        for (end = 0; end < s.length(); ++end) {
            if (mp[s[end]] == 0) ++cnt;
            ++mp[s[end]];
            if (cnt <= 2) res = max(res, end - start + 1);
            while (cnt > 2) {
                --mp[s[start]];
                if (mp[s[start]] == 0) --cnt;
                ++start;
            }
        }
        return res;
    }
};