1. class Solution {
    2.     public String minWindow(String s, String t) {
    3.         HashMap<Character,Integer> need = new HashMap<>();
    4.         HashMap<Character,Integer> window = new HashMap<>();
    5.         for(char ch : t.toCharArray()){
    6.             need.put(ch,need.getOrDefault(ch,0) + 1);
    7.         }
    8.         int left = 0;
    9.         int right = 0;
    10.         int valid = 0;
    11.         int start = 0;
    12.         int len = Integer.MAX_VALUE;
    13.         while(right < s.length()){
    14.             char c = s.charAt(right);
    15.             right++;
    16.             if(need.containsKey(c)){
    17.                 window.put(c,window.getOrDefault(c,0) + 1);
    18.                 ////这个得改成equals
    19.                 if(window.get(c).equals(need.get(c))){
    20.                     valid++;
    21.                 }                                                                                                                      
    22.             }
    23.             while(valid == need.size()){
    24.                 if(right - left < len){
    25.                     start = left;
    26.                     len = right - left;
    27.                 }
    28.                 char d = s.charAt(left);
    29.                 left++;
    30.                 if(need.containsKey(d)){
    31.                     //这个得改成equals
    32.                     if(window.get(d).equals(need.get(d))){
    33.                         valid--; 
    34.                     }
    35.                     window.put(d,window.getOrDefault(d,0) - 1);
    36.                 }
    37.             }
    38.         }
    39.         return len == Integer.MAX_VALUE ? "" : s.substring(start,start + len);
    40.     }
    41. }