<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:
    bool isDivisor(string str1 ,string str2, int len1, int len2, int l){
        if(len1 % l && len2 % l){
            return false;
        }
        int f1 = len1 / l, f2 = len2 / l;
        int i = f1, j = f2;
        string res = "";
        while(i != 0){
            res += str1.substr(0, l);
            i--;
        }
        string res2 = "";
        while(j != 0){
            res2 += str1.substr(0, l);
            j--;
        }
        return res == str1 && res2 == str2;
    }
    string gcdOfStrings(string str1, string str2) {
        int len1 = str1.length(), len2 = str2.length();

        for(int l = min(len1, len2); l > 0; l--){
            if(isDivisor(str1, str2, len1, len2, l)){
                return str1.substr(0, l);
            }
        }
        return "";
    }
};
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