<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 {
private:
    bool check_divisable(string input, string divisor)
    {
        int len = input.length();
        int div_len = divisor.length();
        if (len % div_len)
        {
            return false;
        }
        int checked_len = 0;
        for (int i = 0; i < len; i++)
        {
            if (input[i] != divisor[i % div_len])
            {
                return false;
            }
        }
        return true;
    }   
    int get_shorter_string_index(string &str_1, string &str_2, int *len)
    {
        int len_1 = str_1.length();
        int len_2 = str_2.length();
        if (len_1 < len_2)
        {
            *len = len_1;
            return 0;
        }
        *len = len_2;
        return 1;
}
    
public:
    string gcdOfStrings(string str1, string str2)
    {
        int len = 0;
        string *shorter = &str2;
        string *longer = &str1;
        if(get_shorter_string_index(str1, str2, &len) == 0)
        {
            shorter = &str1;
            longer = &str2;
        }
        for (int i = len; i > 0; i --)
        {
            string divisor = shorter->substr(0, i);
            if (check_divisable(*shorter, divisor) && check_divisable(*longer, divisor))
            {
                return divisor;
            }
        }
        return "";
    }
};
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