<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:
    string gcdOfStrings(string str1, string str2) {
        string key = str1 + "," + str2;
        cout << str1 << " | " << str2 << endl;
        if (str1.size() < str2.size()) {
            cout << "wrong order\n";
            return gcdOfStrings(str2, str1);
        }

        if (str1 == str2) {
            cout << "equal\n";
            return str2;
        }

        for (int i = str2.size(); i > 0; --i) {
            string test_str = str2.substr(0, i);
            cout << "Test str: " << test_str << endl;
            if (str1.find(test_str) == 0) {
                cout << "Match str1\n";
                string out1 = gcdOfStrings(str1.substr(test_str.size()), test_str);
                string out2 = gcdOfStrings(str2.substr(), test_str);
                string result = gcdOfStrings(out1, out2);
                return result;
            }
        }
        return "";
    }
};
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