<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 checkInclusion(string s1, string s2) {
        vector<int> s1_counter(26, 0);
        for (char c : s1) {
            ++s1_counter[c - 'a'];
        }

        int slow = 0;
        int fast = 0;
        vector<int> s2_window_counter(26, 0);
        //s2_window_counter[s2[0] - 'a'];
        while (slow < s2.size()) {
            if (vectorIsSubset(s1_counter, s2_window_counter)) {
                if (fast - slow == s1.size()) {
                    return true;
                }
                --s2_window_counter[s2[slow++] - 'a'];
            }
            else if (fast < s2.size()) {
                ++s2_window_counter[s2[fast++] - 'a'];
            }
            else {
                --s2_window_counter[s2[slow++] - 'a'];
            }
        }

        return false;
    }

private:
    bool vectorIsSubset(vector<int> v1, vector<int> v2) {
        if (v1.size() != v2.size()) {
            return false;
        }
        
        for (int i = 0; i < v1.size(); ++i) {
            if (v1[i] > v2[i]) {
                return false;
            }
        }
    
        return true;
    }
};
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