<p>Given two strings <code>s1</code> and <code>s2</code>, return <code>true</code><em> if </em><code>s2</code><em> contains a permutation of </em><code>s1</code><em>, or </em><code>false</code><em> otherwise</em>.</p>

<p>In other words, return <code>true</code> if one of <code>s1</code>&#39;s permutations is the substring of <code>s2</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s1 = &quot;ab&quot;, s2 = &quot;eidbaooo&quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> s2 contains one permutation of s1 (&quot;ba&quot;).
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s1 = &quot;ab&quot;, s2 = &quot;eidboaoo&quot;
<strong>Output:</strong> false
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s1.length, s2.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s1</code> and <code>s2</code> consist of lowercase English letters.</li>
</ul>

class Solution {
public:
    bool checkEqual(vector<int> a, vector<int> b) {
        for (int i = 0; i < a.size(); i++) {
            if (a[i] != b[i]) {
                return false;
            }
        }
        return true;
    }
    bool checkInclusion(string s1, string s2) {

        if(s1.size() > s2.size()){
            return false;
        }
        vector<int> map(26, 0);

        for (int i = 0; i < s1.length(); i++) {
            int num = s1[i] - 'a';
            map[num]++;
        }

        int i = 0;
        int windowSize = s1.size();
        vector<int> map1(26, 0);
        while (i < windowSize) {
            int index = s2[i] - 'a';
            map1[index]++;
            i++;
        }
        if (checkEqual(map, map1)) {
            return true;
        }

        while (i < s2.size()) {
            int prevIndex = s2[i - windowSize] - 'a';
            map1[prevIndex]--;
            int index = s2[i] - 'a';
            map1[index]++;
            i++;
            if (checkEqual(map, map1)) {
                return true;
            }
        }
        return false;
    }
};
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