public static int diagonalDifference(List<List<int>> arr, int size)
    {
        var lsum = 0;
        var rsum = 0;
        
        for (var xl = 0; xl < size; xl++) {
            lsum += arr[xl][xl];
            rsum += arr[xl][size - 1 - xl];
        }
        
        return Math.Abs(lsum - rsum);
    }