write a go solution for Description:
After winning another Bed Wars game, Masha and Olya wanted to relax and decided to play a new game. Masha gives Olya an array a of length n and a number s. Now Olya's task is to find a non-negative number x such that displaystylesum_i=1^na_ioplusx=s. But she is very tired after a tight round, so please help her with this.

But this task seemed too simple to them, so they decided to make the numbers larger (up to 2^k) and provide you with their binary representation.

Input Format:
Each test consists of several test cases. The first line contains a single integer t (1<=t<=10^4) — the number of test cases. Then follows the description of the test cases.

The first line of each test case contains two integers n and k (1<=n,k,n*k<=2*10^6) — the length of the array a and the length of the binary representation of all numbers.

The second line contains a string of length k, consisting of zeros and ones — the binary representation of the number s, starting from the most significant bits.

The next n lines also contain strings of length k, consisting of zeros and ones, the i-th of these strings contains the binary representation of the number a_i, starting from the most significant bits.

It is guaranteed that the sum of the values n*k for all test cases does not exceed 2*10^6.

Output Format:
For each test case, output a string of length k on a separate line, consisting of zeros or ones — the binary representation of any suitable number x (x>=0), starting from the most significant bits, or -1 if such x does not exist.

Note:
In the first test case, s=11,a=[14,6,12,15], if x=14, then displaystylesum_i=1^na_ioplusx=(14oplus14)+(6oplus14)+(12oplus14)+(15oplus14)=0+8+2+1=11=s.

In the second test case, s=41,a=[191,158], if x=154, then displaystylesum_i=1^na_ioplusx=(191oplus154)+(158oplus154)=37+4=41=s.. Output only the code with no comments, explanation, or additional text.