[leetcode]159. Longest Substring with At Most Two Distinct Characters至多包含两种字符的最长子串

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

Example 1:

Input: "eceba"
Output: 3
Explanation: t is "ece" which its length is 3.

Example 2:

Input: "ccaabbb"
Output: 5
Explanation: t is "aabbb" which its length is 5.

题意：

给定字符串，找出至多包含两种字符的最长子串。

思路：

j          
 “e c e b a”
   i                    e-0
     i                  c-1
         i              e-2
-------map.size()<= 2
            i           b-3  此时移动 j

代码：

 class Solution {
     public int lengthOfLongestSubstringTwoDistinct(String s) {
         if(s.length() < 2) return s.length();
         HashMap<Character, Integer> map = new HashMap<>();
         int result = 0;
         int j = 0;
         for(int i = 0; i < s.length(); ){
             char c = s.charAt(i);
             if(map.size() <= 2){
                 map.put(c, i);
                 i++;
             }
             if(map.size() > 2){
                 int leftMost = s.length();
                 for(int n : map.values()){
                     leftMost = Math.min(leftMost, n);
                 }
                 map.remove(s.charAt(leftMost));
                 j = leftMost + 1;
             }
             result = Math.max(result, i - j );
         }
           return result;
     }
 }