<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) {
        int s1Size = s1.size(), s2Size = s2.size();
        if (s1Size > s2Size) {
            return false;
        }        
        unordered_multiset<char> contained;
        for (const auto& i : s1) {
            contained.emplace(i);
        }
        unordered_multiset<char> containedDifPlus = contained;
        unordered_multiset<char> containedDifMinus;
        unordered_multiset<char> containedStr;
        for (int i = 0; i < s1Size; i++) {
            containedStr.emplace(s2[i]);
        }
        for (const auto& i : containedStr) {
            const auto it = containedDifPlus.find(i);
            if (it != containedDifPlus.end()) {
                containedDifPlus.erase(it);
            } else if (contained.contains(i)) {
                containedDifMinus.emplace(i);
            }
        }
        if (containedDifPlus.empty() && containedDifMinus.empty()) {
            return true;
        }
        for (int i = s1Size, j = 0; i < s2Size; i++, j++) {
            if (contained.contains(s2[j])){
                if (!containedDifMinus.contains(s2[j])) {
                    containedDifPlus.emplace(s2[j]);
                } else {
                    containedDifMinus.erase(containedDifMinus.find(s2[j]));
                }
            }
            if (contained.contains(s2[i])) {
                if (containedDifPlus.contains(s2[i])) {
                    containedDifPlus.erase(containedDifPlus.find(s2[i]));
                } else {
                    containedDifMinus.emplace(s2[i]);
                }
                    
            }
            if (containedDifPlus.empty() && containedDifMinus.empty()) {
                return true;
            }
        }
        return false;
    }
};
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