Repeated String Match

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:** **Input:** a = "abcd", b = "cdabcdab" **Output:** 3 **Explanation:** We return 3 because by repeating a three times "ab**cdabcdab**cd", b is a substring of it. ``` **Example 2:** **Input:** a = "a", b = "aa" **Output:** 2 ```   **Constraints:** - `1 <= a.length, b.length <= 104` - `a` and `b` consist of lowercase English letters.