fn diagonalDifference(arr: &[Vec<i32>]) -> i32 {
    let len = arr.len();
    let (diag_first, diag_second) = (0..len).fold((0, 0), |mut acc, i| {
        acc.0 += arr[i][i];
        acc.1 += arr[i][len - 1 - i];
        acc
    });
    (diag_first - diag_second).abs()
}