hackerrank_csharp_2d_array_hourglass.cs

public static int hourglassSum(List<List<int>> arr)
        {
            var max = -63; // 7 * -9 lower value possible
            for (var i = 0; i < 4; i++) {  // 4 row possibilities
                for (var j = 0; j < 4; j++) // 4 column possibilities
                {
                    var sum = 0;
                    sum = (arr[i][j] + arr[i][j + 1] + arr[i][j + 2] + arr[i + 1][j + 1] + arr[i + 2][j] +
                           arr[i + 2][j + 1] + arr[i + 2][j + 2]);
                    max = max < sum ? sum : max;
                }
            }

            return max;
        }