<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 d = str1.size() > str2.size() ? str2 : str1;
		vector<string> subStrL;
		for (size_t i = 1; i <= d.size(); i++) {
			int foundIdx = 0;
			int count = 0;
			while (foundIdx < d.size()) {
				foundIdx = d.find(d.substr(0, i), foundIdx);
				if (foundIdx == string::npos) break;
				foundIdx += i;
				count++;
			}
			if (count * i == d.size()) {
				subStrL.push_back(d.substr(0, i));
			}
		}
		string d2 = str1.size() > str2.size() ? str1 : str2;
		vector<string> R2;
		for (const string& subS : subStrL) {
			int founIdx = 0;
			int count = 0;
			while (founIdx < d2.size()) {
				founIdx = d2.find(subS, founIdx);
				if (founIdx == string::npos) break;
				founIdx += subS.size();
				count++;
			}
			if (count * subS.size() == d2.size()) {
				R2.push_back(subS);
			}
		}
		string ans;
		for (const string& s : R2) {
			if (ans.size() < s.size()) {
				ans = s;
			}
		}
		return ans;
	}
};
39383