<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) {
        bool str1_shorter = str1.size() < str2.size() ? 1 : 0;
        if (str1_shorter) {
            int count = 0;
            for (int i = 0; i < str1.size(); i++) {
                if (str1[i] == str2[i]) {
                    count++;
                }
                else {
                    break;
                }
            }
            if (count < str1.size()) {
                return string("");
            }
            else {
                for (int i = str1.size(); i >= 1; i--) {
                    if (isDivisor(str1, i, str2) && isDivisor(str1, i, str1)) {
                        return str1.substr(0, i);
                    }
                }
                return string("");
            }
        }
        else {
            int count = 0;
            for (int i = 0; i < str2.size(); i++) {
                if (str1[i] == str2[i]) {
                    count++;
                }
                else {
                    break;
                }
            }
            if (count < str2.size()) {
                return string("");
            }
            else {
                for (int i = str2.size(); i >= 1; i--) {
                    if (isDivisor(str2, i, str1) && isDivisor(str2, i, str2)) {
                        return str2.substr(0,i);
                    }
                }
                return string("");
            }
        }
    }

    bool isDivisor(string div, int cut, string test) {
        int dsize = cut;
        int test_size = test.size();
        if (test_size % dsize != 0) {
            return false;
        }
        for (int i = 0; i < test_size; i++) {
            if (!(test[i] == div[i % dsize]))
                return false;
        }
        return true;
    }
};
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