<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 checker(string str1, string str2) {
        if (str1.length() % str2.length() != 0) return false;
        int step = str2.length();

        int cnt = str1.length() / str2.length();

        //cout << "1: " << str1 << ", " << str2 << endl;

        for (int i = 0; i < cnt; i++) {
            if (str1.substr(i*step, step).compare(str2)) {
                return false;
            }
        }

        //cout << "2: " << str1 << ", " << str2 << endl;

        return true;

    }

    string gcdOfStrings(string str1, string str2) {
        int init_cnt = str2.length();
        string div = str2;
        while (div.length() > 0) {

            if (checker(str1, div)) {
                if (checker(str2, div))
                    return div;
            }
            div.erase(init_cnt--, 1);
 
        }
        return "";

    }
};
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