题解 | #最小覆盖子串#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     * 滑动窗口，用map维护窗口大小
     *
     * @param S string字符串
     * @param T string字符串
     * @return string字符串
     */
    public String minWindow(String str, String target) {
        Map<Character, Integer> map = new HashMap<>();
        for (char charAt : target.toCharArray()) {
            map.put(charAt, map.getOrDefault(charAt, 0) + 1);
        }

        int left = 0, right = 0, start = 0, window = Integer.MAX_VALUE;
        while (right < str.length()) {
            char rightCh = str.charAt(right);
            if (map.containsKey(rightCh)) {
                map.put(rightCh, map.get(rightCh) - 1);
            }
            while (judge(map)) {
                if (right - left + 1 < window) {
                    window = right  - left + 1;
                    start = left;
                }
                char leftCh = str.charAt(left++);
                if (map.containsKey(leftCh)) {
                    map.put(leftCh, map.get(leftCh) + 1);
                }
            }

            right++;
        }
        return window == Integer.MAX_VALUE ? "" : str.substring(start, start + window );
    }

    boolean judge(Map<Character, Integer> map) {
        for (Map.Entry<Character, Integer> entry : map.entrySet()) {
            if (entry.getValue() > 0) {
                return false;
            }
        }
        return true;
    }

}