力扣76.最小覆盖子串

import java.util.HashMap;

//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public String minWindow(String s, String t) {
        int left = 0;
        int right = 0;
        int start = 0;
        int valid = 0;
        int len = Integer.MAX_VALUE;
        Map<Character, Integer> need = new HashMap<>();
        for (int i = 0; i < t.length(); i++) {
            need.put(t.charAt(i), need.getOrDefault(t.charAt(i), 0) + 1);
        }
        Map<Character, Integer> window = new HashMap<>();
        while (right < s.length()) {
            char c = s.charAt(right);
            right++;
            if (need.containsKey(c)) {
                window.put(c, window.getOrDefault(c, 0) + 1);
                if (need.get(c).equals(window.get(c))) {
                    ++valid;
                }
            }
            while (valid == need.size()) {
                if (right - left < len) {
                    len = right - left;
                    start = left;
                }
                char d = s.charAt(left);
                left++;
                if (need.containsKey(d)) {
                    if (window.get(d).equals(need.get(d))) {
                        valid--;
                    }
                    window.put(d, window.get(d) - 1);
                }
            }
        }
        return len == Integer.MAX_VALUE ? "" : s.substring(start, start + len);
    }
}
//leetcode submit region end(Prohibit modification and deletion)