I went for a non-array approach. Feedback much appreciated :)

for(int j = 0; j < numInputs; j++){
    for(int k = 0; k < numInputs; k++){
        cin >> curInput;
        if(j == k){
            leftD += curInput;
        }
        if(j+k == (numInputs-1)){
            rightD += curInput;
        }
    }
}
ans = abs(leftD-rightD);

My solution is to accumulate the mirrored difference in each row like so:

N = int(input())
total = 0
for i in range(N):
    row = input().split()
    total += int(row[i])-int(row[-(i+1)])
print(abs(total))

the only conversions are at two indeces per row regardless of size.

The beauty of python:

d1 = sum([a[x][x] for x in range(n)]) 
d2 = sum([a[x][n-1-x] for x in range (n)])
print(abs(d1-d2))

The input description is not clear at all! If you say it's an array of integers one would assume it's an array of numbers of type integer, something like [42, 66, -5, ...] I had to unlock the solution to find out there are 2 split() functions which operate on strings in JS. WTF! It's not an array of integers but array of strings. Come on! Give proper input description

I see people using nested loops to solve this. I think it is not necessary. Here's my JS code:

var lr = rl = 0;
for(var i = 0; i<n; i++){
    lr += a[i][i];
    rl += a[i][n-i-1];
}  
console.log(Math.abs(lr-rl));