159. Longest Substring with At Most Two Distinct Characters

Same as problem “340. Longest Substring with At Most K Distinct Characters”.

1:  class Solution {  
2:  public:  
3:    int lengthOfLongestSubstringTwoDistinct(string s) {  
4:      int i = 0, j = -1;  
5:      vector<int> dict(256, 0);  
6:      int len = 0;  
7:      int k = 0;  
8:      while (i < s.size()) {  
9:        k += dict[s[i]]++ == 0;  
10:        while (k > 2) k -= --dict[s[++j]] == 0;  
11:        len = max(len, i-j);  
12:        i++;  
13:      }  
14:      return len;  
15:    }  
16:  };