B. Infinite Prefixestime limit per test2 secondsmemory limit per test256 megabytesinputstandard inputoutputstandard outputYou are given string s of length n consisting of 0-s and 1-s. You build an infinite string t as a concatenation of an infinite number of strings s, or t = ssss \dots For example, if s = 10010, then t = 100101001010010...Calculate the number of prefixes of t with balance equal to x. The balance of some string q is equal to cnt_{0, q} - cnt_{1, q}, where cnt_{0, q} is the number of occurrences of 0 in q, and cnt_{1, q} is the number of occurrences of 1 in q. The number of such prefixes can be infinite; if it is so, you must say that.A prefix is a string consisting of several first letters of a given string, without any reorders. An empty prefix is also a valid prefix. For example, the string "abcd" has 5 prefixes: empty string, "a", "ab", "abc" and "abcd".InputThe first line contains the single integer T (1 \le T \le 100) — the number of test cases.Next 2T lines contain descriptions of test cases — two lines per test case. The first line contains two integers n and x (1 \le n \le 10^5, -10^9 \le x \le 10^9) — the length of string s and the desired balance, respectively.The second line contains the binary string s (|s| = n, s_i \in \{\text{0}, \text{1}\}).It's guaranteed that the total sum of n doesn't exceed 10^5.OutputPrint T integers — one per test case. For each test case print the number of prefixes or -1 if there is an infinite number of such prefixes.ExampleInput
4
6 10
010010
5 3
10101
1 0
0
2 0
01
Output
3
0
1
-1
NoteIn the first test case, there are 3 good prefixes of t: with length 28, 30 and 32.
4
6 10
010010
5 3
10101
1 0
0
2 0
01

3 0 1 -1 
['math', 'strings', '*1700']