# [LintCode] Permutation in String

### 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"
Output:True
Explanation: s2 contains one permutation of s1 ("ba").
Example 2:

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

### 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;
}
}
``````