<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(string s) {
        int max_substr_len = s.length() / 2;
        if (max_substr_len < 1) return false;

        for (int len = max_substr_len; len >= 1; len--) {
            string sub_str = s.substr(0, len);
            int copy_count = (s.length() / len);
            if (copy_count * len == s.length()) {
                string copy_str = multiAppend(sub_str, copy_count);
                if (copy_str.compare(s) == 0) {
                    return true;
                }
            }
        }

        return false;
    }

    string multiAppend(string a,  int count) {
        if (count == 0) {
            return "";
        }
        return a + multiAppend(a, count-1);
    }
};
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