Euler18.cs

// Find the maximum total from top to bottom of the triangle below:

using System;

class Program
{
    static void Main()
    {
        var triangle = new int[][]
        {
            new[]                          {75},
            new[]                        {95, 64},
            new[]                      {17, 47, 82},
            new[]                    {18, 35, 87, 10},
            new[]                  {20, 04, 82, 47, 65},
            new[]                {19, 01, 23, 75, 03, 34},
            new[]              {88, 02, 77, 73, 07, 63, 67},
            new[]            {99, 65, 04, 28, 06, 16, 70, 92},
            new[]          {41, 41, 26, 56, 83, 40, 80, 70, 33},
            new[]        {41, 48, 72, 33, 47, 32, 37, 16, 94, 29},
            new[]       {53, 71, 44, 65, 25, 43, 91, 52, 97, 51, 14},
            new[]     {70, 11, 33, 28, 77, 73, 17, 78, 39, 68, 17, 57},
            new[]   {91, 71, 52, 38, 17, 14, 91, 43, 58, 50, 27, 29, 48},
            new[] {63, 66, 04, 68, 89, 53, 67, 30, 73, 16, 69, 87, 40, 31},
            new[]{04, 62, 98, 27, 23, 09, 70, 98, 73, 93, 38, 53, 60, 04, 23}
        };
        
        for (int i = triangle.Length - 2; i >= 0; i--)
            for (int k = 0; k < triangle[i].Length; k++)
                triangle[i][k] += Math.Max(
                    triangle[i + 1][k], 
                    triangle[i + 1][k + 1]);

        Console.WriteLine(triangle[0][0]);
    }
}