Diagonal Difference^Easy

Given a square matrix, calculate the absolute difference between the sums of its diagonals.

For example, the square matrix \(arr\) is shown below:
1 2 3
4 5 6
9 8 9
The left-to-right diagonal: \(1 + 5 + 9 = 15\).

The right-to-left diagonal: \(3 + 5 + 9 = 17\).

Their absolute difference is \(|15 - 17| = 2\).