Problem

Given two strings s1 and s2, write a function to return true if s2 contains the permutation of s1. In other words, one of the first string's permutations is the substring of the second string.

Example

Example 1:

Input:s1 = "ab" s2 = "eidbaooo"

Input:s1= "ab" s2 = "eidboaoo"

Solution

public class Solution {    /**     * @param s1: a string     * @param s2: a string     * @return: if s2 contains the permutation of s1     */    public boolean checkInclusion(String s1, String s2) {        int len = s1.length();        for (int i = 0; i <= s2.length()-len; i++) {            if (isPermutation(s2.substring(i, i+len), s1)) return true;        }        return false;    }        //use the method of #String Permutation    public boolean isPermutation(String s1, String s2) {        if (s1 == null) return s2 == null;        if (s2 == null) return s1 == null;        if (s1.length() != s2.length()) return false;                int[] dict = new int[256];        char[] c1 = s1.toCharArray();        char[] c2 = s2.toCharArray();        for (char ch: c1) {            dict[(int)ch]++;        }        for (char ch: c2) {            dict[(int)ch]--;            if (dict[(int)ch] < 0) return false;        }        return true;    }}