[leetcode]340. Longest Substring with At Most K Distinct Characters至多包含K种字符的最长子串

Given a string, find the length of the longest substring T that contains at most k distinct characters.

For example, Given s = “eceba” and k = 2,

T is "ece" which its length is 3.

题意：

给定字符串，求至多包含K种字符的最长子串

思路：

跟[leetcode]159. Longest Substring with At Most Two Distinct Characters至多包含两种字符的最长子串思路大体相同

      j
    j
S= “e c e b a”    and k = 2,  return 3  for "e c e"
    i             e-0          map.size <=2  move i 
      i           c-1          map.size <=2  move i 
        i         e-2(update)  map.size <=2  move i 
 ---------        b-3          map.size >2   get the length then move j 
          i  

代码：

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