# Permutation In String Problem

## Description

LeetCode Problem 567.

Given two strings s1 and s2, return true if s2 contains a permutation of s1, or false otherwise. In other words, return true if one of s1’s permutations is the substring of s2.

Example 1:

``````1
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Input: s1 = "ab", s2 = "eidbaooo"
Output: true
Explanation: s2 contains one permutation of s1 ("ba").
``````

Example 2:

``````1
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Input: s1 = "ab", s2 = "eidboaoo"
Output: false
``````

Constraints:

• 1 <= s1.length, s2.length <= 10^4
• s1 and s2 consist of lowercase English letters.

## Sample C++ Code

``````1
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class Solution {
public:
bool checkInclusion(string s1, string s2) {
int l1 = s1.size(), l2 = s2.size();
if (l1 > l2) return false;

vector<int> m(26, 0);

for (int i = 0; i < l1; i ++) {
m[s1[i] - 'a'] ++;
m[s2[i] - 'a'] --;
}

bool contained = true;
for (int i = 0; i < 26; i ++) {
if (m[i] != 0) {
contained = false;
break;
}
}
if (contained) return true;

for (int i = l1; i < l2; i ++) {
m[s2[i] - 'a'] --;
m[s2[i-l1] - 'a'] ++;

contained = true;
for (int j = 0; j < 26; j ++) {
if (m[j] != 0) {
contained = false;
break;
}
}
if (contained) return true;

}

return false;
}
};
``````