686. Repeated String Match

Given two strings A and B, find the minimum number of times A has to be repeated such that B is a substring of it. If no such solution, return -1.

For example, with A = "abcd" and B = "cdabcdab".

Return 3, because by repeating A three times (“abcdabcdabcd”), B is a substring of it; and B is not a substring of A repeated two times ("abcdabcd").

Note:
The length of A and B will be between 1 and 10000.

class Solution {

    public int repeatedStringMatch(String A, String B) {

        int count = 0;

        StringBuilder sb = new StringBuilder();

        while (sb.length() < B.length()) {

            sb.append(A);

            count++;

        }

        if (sb.toString().contains(B))

            return count;

        if (sb.append(A).toString().contains(B)) //关键在于还要再repeat一次，之后就没有必要再repeat了

            return ++count;

        return -1;

    }

}