public static int diagonalDifference(List<List<int>> arr)
    {
        int left = 0;
        int right = 0 ;
        int indexRight = arr.Count();
        
        
        for(int x=0; x < arr.Count(); x ++){
            indexRight --;
            left += arr[x][x];
            right += arr[x][indexRight];
        }
        
        if(left > right)
            return left - right;
        else
            return right - left;
    }