<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) {
        if(b == "") return 0;
        if(a.size() >= b.size()){
            int tmp = a.size();
            a += a;
            for(int i = 0; i + b.size() - 1 < a.size(); i++){
                if(a.substr(i, b.size()) == b) return (i + b.size() - 1 < tmp)? 1 : 2;
            }
            return -1;
        }
        int index = 0, ans = 1; bool f = false;
        for(int i = 0; i < a.size(); i++){
            if(a.substr(i, a.size() - i) == b.substr(0, a.size() - i)){
                index = a.size() - i;
                f = true;
                break;
            }
        }
        if(!f) return -1;
        while(index + a.size() - 1 < b.size()){
            if(b.substr(index, a.size()) == a){
                ans++;
                index = index + a.size();
            }
            else{
                return -1;
            }
        }
        if(index == b.size()) return ans;
        if(b.substr(index, b.size() - index) == a.substr(0, b.size() - index)){
            return ans + 1;
        }
        return -1;
    }
};
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