# Repeated String Match Problem

## Description

LeetCode Problem 686.

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

Notice: string “abc” repeated 0 times is “”, repeated 1 time is “abc” and repeated 2 times is “abcabc”.

Example 1:

``````1
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3
Input: a = "abcd", b = "cdabcdab"
Output: 3
Explanation: We return 3 because by repeating a three times "abcdabcdabcd", b is a substring of it.
``````

Example 2:

``````1
2
Input: a = "a", b = "aa"
Output: 2
``````

Example 3:

``````1
2
Input: a = "a", b = "a"
Output: 1
``````

Example 4:

``````1
2
Input: a = "abc", b = "wxyz"
Output: -1
``````

Constraints:

• 1 <= a.length <= 10^4
• 1 <= b.length <= 10^4
• aandbconsist of lower-case English letters.

## Sample C++ Code

``````1
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class Solution {
public:
int repeatedStringMatch(string A, string B) {
int len_a = A.size();
int len_b = B.size();
int n = len_b / len_a + 2; // 1 is for the round up, 1 is for 1 more repeat
int i;
string r_A = A;
for (i = 1; i <= n; i ++) {
if (r_A.find(B) != string::npos) {
return i;
} else {
r_A += A;
}
}
return -1;
}
};
``````