1 public class Solution { 2     public int lengthOfLongestSubstringKDistinct(String s, int k) { 3         if (k == 0) { 4             return 0; 5         } 6          7         Map
     
       letters = new HashMap<>(); 8         int result = 0; 9         int count = 0;10         for (int left = 0, right = 0; right < s.length(); right++) {11             letters.put(s.charAt(right), letters.getOrDefault(s.charAt(right), 0) + 1);12             if (letters.get(s.charAt(right)) == 1) {13                 count++;14             }15             16             if (count > k) {17                 while (left < right && letters.get(s.charAt(left)) > 0) {18                     int current = letters.get(s.charAt(left));19                     letters.put(s.charAt(left++), current - 1);20                     if (current == 1) {21                         count--;22                         break;23                     }24                 }25             }26             27             result = Math.max(result, right - left + 1);28         }29         return result;30     }31 }
     

1. put element do not forget to + 1

2. do not forget left move left++.