[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;  
    }
}