<p>Given a string <code>s</code>, check if it can be constructed by taking a substring of it and appending multiple copies of the substring together.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abab&quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> It is the substring &quot;ab&quot; twice.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;aba&quot;
<strong>Output:</strong> false
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abcabcabcabc&quot;
<strong>Output:</strong> true
<strong>Explanation:</strong> It is the substring &quot;abc&quot; four times or the substring &quot;abcabc&quot; twice.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s</code> consists of lowercase English letters.</li>
</ul>

class Solution {
public:
    bool repeatedSubstringPattern(const std::string& str)
	{
		const int length = str.length();
		const int halfLength = length / 2;

		char first = str[0];
		int patternLength = 1;
		while (patternLength <= halfLength)
		{
			while (patternLength <= halfLength && str[patternLength] != first)
				++patternLength;

			std::string pattern = str.substr(0, patternLength);
			if (patternLength != length && length % patternLength == 0)	// is candidate valid
			{
				int i = patternLength;
				while (i <= length - patternLength && str.substr(i, patternLength) == pattern)
					i += patternLength;

				if (i == length)
					return true;
			}
			++patternLength;
		}

		return false;
	}
};
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