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 "abcdabcdabcd", b is a substring of it. Example 2: Input: a = "a", b = "aa" Output: 2 Example 3: Input: a = "a", b = "a" Output: 1 Example 4: Input: a = "abc", b = "wxyz" Output: -1 Constraints: 1 <= a.length <= 104 1 <= b.length <= 104 a and b consist of lower-case English letters.