<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 ret_str;
        string shortest_str = str1.size() < str2.size() ? str1 : str2;
        auto size = shortest_str.size();
        while (ret_str.empty() && size > 0) {
            string str1_copy = str1;
            string str2_copy = str2;
            auto current_str = shortest_str.substr(0, size);
            size_t pos;
            while ((pos = str1_copy.find(current_str)) == 0) {
                str1_copy.erase(pos, current_str.length());
            }
            while ((pos = str2_copy.find(current_str)) == 0) {
                str2_copy.erase(pos, current_str.length());
            }
            if (str1_copy.empty() && str2_copy.empty()) {
                ret_str = current_str;
            }
            size--;
        }
        return ret_str;
    }
};
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