<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(const std::string& str, const std::string& divisor) {
        if (str == divisor) {
            return true;
        }

        if (str.size() % divisor.size() != 0) {
            return false;
        }

        int64_t parts_count = str.size() / divisor.size();
        std::string tmp;

        while (parts_count-- > 0) {
            tmp += divisor;
        }

        return str == tmp;
    }
    string gcdOfStrings(string str1, string str2) {

        if (str1.size() > str2.size()) {
            std::swap(str1, str2);
        }
        
        if (isDivisor(str2, str1)) {
            return str1;
        }

        int i = 0;

        while (i < str1.size() / 2 && str1[i] == str2[i]) {
            ++i;
        }

        if (i == 0) {
            return "";
        }

        while (i > 0) {
            const std::string divisor = str1.substr(0, i);

            if (isDivisor(str1, divisor) && isDivisor(str2, divisor)) {
                return divisor;
            }

            --i;
        }

        return "";
    }
};
12001