最小覆盖子串

 public String minWindow(String s, String t) {

        HashMap<Character,Integer> need = new HashMap();

        HashMap<Character,Integer> window = new HashMap();

        for(int i = 0;i<t.length();i++){

            int count = need.getOrDefault(t.charAt(i),0);

            need.put(t.charAt(i), count + 1);

        }

        int left = 0;

        int right = 0;

        int match = 0;

        int min = Integer.MAX_VALUE;

        int start = 0;

        while(right < s.length()){

            char c = s.charAt(right);

            right++;

            if(need.containsKey(c)){

               int cou =  window.getOrDefault(c,0);

               window.put(c,cou + 1);

               if(window.get(c).equals(need.get(c))){

                   match++;

               }

            }

            while(match == need.size()){

                if((right - left) <min){

                    min = right - left;

                    start = left;

                }

                char d = s.charAt(left);

                left++;

                if(need.containsKey(d)){

                    int ccccc = window.get(d);

                    if(window.get(d).equals(need.get(d))){

                        match--;

                    }

                    window.put(d,ccccc-1);

                }

            }

        }

        return min == Integer.MAX_VALUE? "":s.substring(start,start +min );

    }