<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:
    unordered_map<char, int> s1Map;
    bool checkInclusion(string s1, string s2) {
        if (s1.length() > s2.length())
            return false;

        for(char c: s1) {
            s1Map[c]++;
        }
        int n = s2.length() - s1.length();
        //Iterate over s2
        for(int i=0; i<=n; i++) {
            char c = s2[i];
            if(s1Map.find(c) != s1Map.end()) {
                // substring starting at c might be a permutation
                if(checkifPermutation(s2.substr(i, s1.length()))) {
                    return true;
                }
            }
        }
        return false;
    }

    bool checkifPermutation(string s2) {
        // cout << s2 << endl;
        unordered_map<char, int> s2Map;
        for(char c:s2) {
            s2Map[c]++;
        }

        // cout << s1Map.size() << " " << s2Map.size() << endl;
        if(s1Map.size() != s2Map.size()) return false;

        
        for(auto it : s1Map) {
            // cout << it.first << " " << it.second << endl;
            if(it.second != s2Map[it.first]) return false;
        }
    
        return true;
    }
};
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