<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 {
    void lpsarray(string patern, vector<int>&lps){
        for(int i=1;i<patern.size();i++){
            int j = lps[i-1];
            while(j>0 && patern[i]!=patern[j]){
                j = lps[j-1];
            }
            if(patern[i]==patern[j]){
                j++;
            }
            lps[i] =j;
        }
    }
    bool kmp(string s, string patern){
        int n =s.size();
        vector<int>lps(patern.size(),0);
        lpsarray(patern,lps);
        int i=0,j=0;
        while(i<s.size()){
            if(s[i]==patern[j]){
                i++;
                j++;
            }
            else{
                if(j!=0) j = lps[j-1];
                else i++;
            }
            if(j==patern.size()){
                return true;
            }
        }
        return false;
    }
public:
    int repeatedStringMatch(string a, string b) {
        int len_a = a.size();
        int len_b = b.size();
        int n = len_b/len_a;
        int cnt = n;
        string s="";
        while(cnt--){
            s = s+a;
        }
        if(kmp(s,b)) return n;
        s+=a;
        if(kmp(s,b)) return n+1;
        s+=a;
        if(kmp(s,b)) return n+2;
        return -1;
    }
};
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