[LeetCode] Longest Substring with At Most Two Distinct Characters

 1 class Solution {
 2 public:
 3     int lengthOfLongestSubstringTwoDistinct(string s) {
 4         int res = 0, start = 0, end = 0;
 5         vector<int> mp(256, 0);
 6         int cnt = 0;
 7         for (end = 0; end < s.length(); ++end) {
 8             if (mp[s[end]] == 0) ++cnt;
 9             ++mp[s[end]];
10             if (cnt <= 2) res = max(res, end - start + 1);
11             while (cnt > 2) {
12                 --mp[s[start]];
13                 if (mp[s[start]] == 0) --cnt;
14                 ++start;
15             }
16         }
17         return res;
18     }
19 };