Maximum triangle path sum

Starting from the top of a pyramid of numbers like this, you can walk down going one step on the right or on the left, until you reach the bottom row:

                          55
                        94 48
                       95 30 96
                     77 71 26 67

One of such walks is 55 - 94 - 30 - 26. You can compute the total of the numbers you have seen in such walk, in this case it's 205.

Maximum triangle path sum is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Your problem is to find the maximum total among all possible paths from the top to the bottom row of the triangle. In the little example above it's 321.

Task: find the maximum total in the triangle below:

                          55
                        94 48
                       95 30 96
                     77 71 26 67
                    97 13 76 38 45
                  07 36 79 16 37 68
                 48 07 09 18 70 26 06
               18 72 79 46 59 79 29 90
              20 76 87 11 32 07 07 49 18
            27 83 58 35 71 11 25 57 29 85
           14 64 36 96 27 11 58 56 92 18 55
         02 90 03 60 48 49 41 46 33 36 47 23
        92 50 48 02 36 59 42 79 72 20 82 77 42
      56 78 38 80 39 75 02 71 66 66 01 03 55 72
     44 25 67 84 71 67 11 61 40 57 58 89 40 56 36
   85 32 25 85 57 48 84 35 47 62 17 01 01 99 89 52
  06 71 28 75 94 48 37 10 23 51 06 48 53 18 74 98 15
27 02 92 23 08 71 76 84 15 52 92 63 81 10 44 10 69 93

This task is derived from the Euler Problem #18.

D

This solution assumes the triangle is in a "triangle.txt" file.

<lang d>void main() {

   import std.stdio, std.algorithm, std.range, std.file, std.conv;

   "triangle.txt".File.byLine.map!split.map!(to!(int[])).array.retro
   .reduce!((x, y) => zip(y, x, x.dropOne)
                      .map!(t => t[0] + t[1 .. $].max)
                      .array)[0]
   .writeln;

}</lang>

Output:

1320