滑动窗口-最小子串

package slidewindow;

import java.util.HashSet;
import java.util.Set;

public class MinSubstring {

    static String minWindow(String s, String t) {
        // 参数校验
        if (s.length() < 1 || t.length() < 1) {
            return "";
        }
        Set<Character> needed = new HashSet<>();
        for (Character c : t.toCharArray()) {
            needed.add(c);
        }
        Set<Character> window = new HashSet<>();
        // 窗口游标初始化
        int left = 0, right = 0;
        // 记录最小覆盖子串的起始游标及长度
        int start = 0, len = Integer.MAX_VALUE;
        while (right < s.length()) {
            if (needed.contains(s.charAt(right))) {
                window.add(s.charAt(right));
            }
            right++;
            // 窗口满足收缩条件
            while (window.size() == needed.size()) {
                if (right - left < len) {
                    start = left;
                    len = right - left;
                }
                window.remove(s.charAt(left));
                left++;
            }
        }
        return len == Integer.MAX_VALUE ? ""
                : s.substring(start, start + len);
    }

    public static void main(String[] args) {
        String a = minWindow("bcss", "bc");
    }

}