Minimum Adjacent Swaps to Equalize Binary Strings

Given two binary strings a and b of equal length, determine the minimum number of adjacent swaps required to transform string a into string b. In each swap, only two adjacent characters can be exchanged.

Note: The transformation is possible only if both strings have the same number of '1' characters.

For example:

• If a = "1100" and b = "1001", the answer is 2.
• If a = "10101" and b = "10110", the answer is 1.
• If a = "111" and b = "111", the answer is 0.
• If the number of '1' characters differ (e.g. a = "1100" and b = "1110"), output -1.

inputFormat

The input begins with an integer T (T ≥ 1), representing the number of test cases. Each test case consists of two lines:

• The first line contains the binary string a.
• The second line contains the binary string b (with the same length as a).

outputFormat

For each test case, output a single integer: the minimum number of adjacent swaps required to transform a into b. If the transformation is impossible, output -1. Each answer should be printed on its own line.

## sample

6
1100
1001
10101
10110
111
111
1100
1110
100
000
10
01

2
1
0
-1
-1
1

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