Tradelab freshers hiring challenge skillenza-question1

"""
Bit Swapping
You’re given a pair of matrices having the same size i.e. the same number of rows and the same number of columns. Each matrix element is a bit either 0 or 1. 
The objective is to find the minimum number of positional swaps that are required in the first matrix in order for its arrangement to match that of the second.
If the arrangement can never be matched, output -1. A swap is an exchange of element values for a row and column combination with another row and column combination.

Input Format
The first line contains a single integer t, denoting the number of test cases.
The first line of each test case contains two space separated integers m and n denoting the number of rows and number of columns. 
Next m lines each contains n elements of the first matrix. Next m lines each contains n elements of the second matrix.

Output Format
For each test case print the minimum swaps.

Constraints
1 <= t <= 1000

1 <= m <= 100

1 <= n <= 100

Sample Input
6
2 2
00
11
01
10
2 2
00
11
00
11
2 2
00
11
01
00
1 7
0011011
0101101
1 1
0
1
1 1
0
0


Sample Output
1
0
-1
2
-1
0
"""

t=int(input())
for i in range(0,t):
    l=list(map(int,input().split()))
    m=l[0]
    n=l[1]
    l1=[]
    l2=[]
    one=0
    zero=0
    for j in range(0,m):
        l1.append(input())
    for j in range(0,m):
        l2.append(input())
    for j in range(0,m):
        first=l1[j]
        last=l2[j]
        for k in range(0,len(first)):
            if(first[k]==last[k]):
                pass
            else:
                if(first[k]=='1'):
                    one+=1
                else:
                    zero+=1
    if(zero==one and zero!=0):
        print(zero)
    if(zero==0 and one==0):
        print("0")
    if(zero!=one):
        print("-1")