leetcode

LeetCode 567. Permutation in String

Problem

LeetCode 567. Permutation in String

1. 题目简述

给出两个字符串s1和s2，判断s2中是否含有s1所有字母的一组排列。例如：

Input: s1 = "ab" s2 = "eidbaooo"
Output: True
Explanation: s2 contains one permutation of s1 ("ba").

2. 算法思路

sliding window

这道题和LeetCode-438基本一致，算法也一模一样，只是返回的内容不同，这道题还性对简单点，同样是使用两个数组来记录字母个数，每次滑动窗口时判断是否和目标字母一致。

3. 解法

  1. 双数组

class Solution {
    public boolean checkInclusion(String s1, String s2) {
        if (s1.length() > s2.length()) {
            return false;
        }

        int[] dict = new int[26];
        int[] window = new int[26]; 

        for (int i = 0; i < s1.length(); i++) {
            char c = s1.charAt(i);
            dict[c - 'a']++;
        }

        int start = 0, end = 0;
        for (; end < s1.length(); end++) {
            char c = s2.charAt(end);
            window[c - 'a']++;
        }

        boolean flag = true;
        for (int i = 0; i < 26; i++) {
            if (dict[i] != window[i]) {
                flag = false;
                break;
            }
        }

        if (flag) {
            return true;
        }

        for (start = 1; end < s2.length(); start++, end++) {
            window[s2.charAt(start - 1) - 'a']--;
            window[s2.charAt(end) - 'a']++;
            flag = true;
            for (int i = 0; i < 26; i++) {
                if (dict[i] != window[i]) {
                    flag = false;
                    break;
                }
            }
            if (flag) {
                return true;
            }
        }

        return false;
    }
}