<p>Given two strings <code>a</code> and <code>b</code>, return <em>the minimum number of times you should repeat string </em><code>a</code><em> so that string</em> <code>b</code> <em>is a substring of it</em>. If it is impossible for <code>b</code>​​​​​​ to be a substring of <code>a</code> after repeating it, return <code>-1</code>.</p>

<p><strong>Notice:</strong> string <code>&quot;abc&quot;</code> repeated 0 times is <code>&quot;&quot;</code>, repeated 1 time is <code>&quot;abc&quot;</code> and repeated 2 times is <code>&quot;abcabc&quot;</code>.</p>

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

<pre>
<strong>Input:</strong> a = &quot;abcd&quot;, b = &quot;cdabcdab&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> We return 3 because by repeating a three times &quot;ab<strong>cdabcdab</strong>cd&quot;, b is a substring of it.
</pre>

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

<pre>
<strong>Input:</strong> a = &quot;a&quot;, b = &quot;aa&quot;
<strong>Output:</strong> 2
</pre>

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

<ul>
	<li><code>1 &lt;= a.length, b.length &lt;= 10<sup>4</sup></code></li>
	<li><code>a</code> and <code>b</code> consist of lowercase English letters.</li>
</ul>

class Solution {
public:
    int repeatedStringMatch(string a, string b) {
        return repeatedStringMatchHelper(a, b, "", 0);
    }

private:
    int repeatedStringMatchHelper(const string &a, const string &b, string str, int count) {
        str += a;
        count++;
        
        if (isSubstring(str, b)) {
            return count;
        }
        
        if (str.length() < b.length() + a.length()) {
            return repeatedStringMatchHelper(a, b, str, count);
        }

        return -1;
    }

    bool isSubstring(const string &str, const string &b) {
        int strLen = str.length();
        int bLen = b.length();

        for (int i = 0; i <= strLen - bLen; ++i) {
            int j;
            for (j = 0; j < bLen; ++j) {
                if (str[i + j] != b[j]) {
                    break;
                }
            }
            if (j == bLen) {
                return true;
            }
        }
        return false;
    }
};
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