159 Longest Substring with At Most Two Distinct Characters

来源：Leetcode

原帖：https://oj.leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/

题目：
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.

代码：

 class Solution {  
   int lengthOfLongestSubstringTwoDistinct(string s) {  
     int res = 0, count = 0;  
     vector<int> need(256, 0);  
     int i = 0, j = 0;  
     while (j < s.size()) {  
       if (need[s[j]] == 0) count++;  
       need[s[j]]++;  
       if (count <= 2) {  
         j++;   
         continue;  
       }  
       res = max(res, j - i);  
       while (i < j && count == 3) {  
         need[s[i]]--;  
         if (need[s[i]] == 0) count--;  
         i++;  
       }  
       j++;  
     }  
     res = max(res, j - i);  
     return res;  
   }  
 }