leetcode-567 字符串的排列

题目描述：给你两个字符串 s1 和 s2 ，写一个函数来判断 s2 是否包含 s1 的排列。

换句话说，s1 的排列之一是 s2 的 子串 。

代码实现

class Solution {
    public boolean checkInclusion(String s1, String s2) {
        Map<Character, Integer> need = new HashMap<>();
        Map<Character, Integer> window = new HashMap<>();
        for (int i = 0; i < s1.length(); i++) {
            need.merge(s1.charAt(i), 1, (oldVal, newVal) -> ++oldVal);
        }

        int left = 0, right = 0, valid = 0;
        while (right < s2.length()) {
            char r = s2.charAt(right);
            right++;
            if (need.containsKey(r)) {
                window.merge(r, 1, (oldVal, newVal) -> ++oldVal);
                if (window.get(r).equals(need.get(r))) {
                    valid++;
                }
            }

            while (right - left == s1.length()) {
                if (valid == need.size()) {
                    return true;
                }
                char l = s2.charAt(left);
                left++;
                if (need.containsKey(l)) {
                    if (window.get(l).equals(need.get(l))) {
                        valid--;
                    }
                    window.compute(l, (k, v) -> --v);
                }
            }
        }
        return false;
    }
}