<p>For two strings <code>s</code> and <code>t</code>, we say &quot;<code>t</code> divides <code>s</code>&quot; if and only if <code>s = t + t + t + ... + t + t</code> (i.e., <code>t</code> is concatenated with itself one or more times).</p>

<p>Given two strings <code>str1</code> and <code>str2</code>, return <em>the largest string </em><code>x</code><em> such that </em><code>x</code><em> divides both </em><code>str1</code><em> and </em><code>str2</code>.</p>

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

<pre>
<strong>Input:</strong> str1 = &quot;ABCABC&quot;, str2 = &quot;ABC&quot;
<strong>Output:</strong> &quot;ABC&quot;
</pre>

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

<pre>
<strong>Input:</strong> str1 = &quot;ABABAB&quot;, str2 = &quot;ABAB&quot;
<strong>Output:</strong> &quot;AB&quot;
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> str1 = &quot;LEET&quot;, str2 = &quot;CODE&quot;
<strong>Output:</strong> &quot;&quot;
</pre>

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

<ul>
	<li><code>1 &lt;= str1.length, str2.length &lt;= 1000</code></li>
	<li><code>str1</code> and <code>str2</code> consist of English uppercase letters.</li>
</ul>

class Solution {
public:
    list<string> factorOfString(string str){
        int strSize = str.size();
        list<string> factors;
        for(int i=1;i<=(strSize)/2;i++){
            string substring = str.substr(0,i);
            int flag = 1;
            if(strSize%i!=0)
                continue;
            for(int j=2;j<=strSize/i;j++){
                if(substring != str.substr(i*(j-1), i)){
                    flag = 0;
                    break; 
                }
            }
            if(flag){
                factors.push_back(substring);
            }
        }
        factors.push_back(str);
        return factors;
    }
    string gcdOfStrings(string str1, string str2) {
        list<string> factor1 = Solution().factorOfString(str1);
        list<string> factor2 = Solution().factorOfString(str2);
        for (auto it = factor1.rbegin(); it != factor1.rend(); ++it){
            for(auto it2=factor2.rbegin(); it2 != factor2.rend(); ++it2){
                if((*it).compare(*it2)==0)
                    return *it;
                else if((*it2).size()<(*it).size())
                    break;
            }
        }
        return "";
        
    }
};
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