<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 {
    bool divide(string str1, string str2, string prefix)
    {
        while(str1.length() > 0)
        {
            if(str1.substr(0, prefix.length()) == prefix)
            {
                str1.erase(0, prefix.length());
            }
            else
            {
                return false;
            }

            
        }
         while(str2.length() > 0)
        {
            if(str2.substr(0, prefix.length()) == prefix)
            {
                str2.erase(0, prefix.length());
            }
            else
            {
                return false;
            }

            
        }
        return true;

    }
public:
    string gcdOfStrings(string str1, string str2) {
        int i = 0;
        string prefix = "";
        while(1)
        {
            if(i == str1.length() || i == str2.length())
            {
                break;
            }
            if(str1[i] != str2[i])
            {
                break;
            }
            prefix += str1[i++];
        }
        string copy1 = str1;
        string copy2 = str2;
        
        while(prefix.length() > 0)
        {
            while(str1.length()%prefix.length() != 0 && str2.length()%prefix.length() != 0)
            {
                prefix.pop_back();
            }
            if(divide(str1,str2, prefix))
            {
                return prefix;
            }
            prefix.pop_back();
        }
        return prefix;
    }
};
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