p018.erl

%% Solution for Project Euler prolem 018

-module(p018).
-export([solve/0]).

tri() -> [[75],
          [95, 64],
          [17, 47, 82],
          [18, 35, 87, 10],
          [20, 04, 82, 47, 65],
          [19, 01, 23, 75, 03, 34],
          [88, 02, 77, 73, 07, 63, 67],
          [99, 65, 04, 28, 06, 16, 70, 92],
          [41, 41, 26, 56, 83, 40, 80, 70, 33],
          [41, 48, 72, 33, 47, 32, 37, 16, 94, 29],
          [53, 71, 44, 65, 25, 43, 91, 52, 97, 51, 14],
          [70, 11, 33, 28, 77, 73, 17, 78, 39, 68, 17, 57],
          [91, 71, 52, 38, 17, 14, 91, 43, 58, 50, 27, 29, 48],
          [63, 66, 04, 68, 89, 53, 67, 30, 73, 16, 69, 87, 40, 31],
          [04, 62, 98, 27, 23, 09, 70, 98, 73, 93, 38, 53, 60, 04, 23]].

lsum(L1, L2) -> lists:zipwith(fun(A, B) -> A + B end,  L1, L2).

rowmax(L) -> [lists:max(lists:sublist(L, Start, 2)) || 
              Start <- lists:seq(1, length(L) - 1)].

maxpathsum(T) -> hd(lists:foldl(fun(A, B) -> lsum(A, rowmax(B)) end, 
                 lists:duplicate(length(T) + 1,0), lists:reverse(T))).

solve() -> maxpathsum(tri()).