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c5eb97d Jan 23, 2017
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{-
- Solution to Project Euler problem 18
- Copyright (c) Project Nayuki. All rights reserved.
-
- https://www.nayuki.io/page/project-euler-solutions
- https://github.com/nayuki/Project-Euler-solutions
-}
{-
- If we start at a particular cell in the triangle, what is the maximum path total?
- If the cell is in the bottom row, then it is simply the cell's value. Otherwise the answer
- is the cell's value plus either {the maximum path total of the cell down and to the left}
- or {the maximum path total of the cell down and to the right}, whichever is greater.
-}
main = putStrLn (show ans)
ans = maxPath 0 0
maxPath i j = (triangle !! i !! j) +
(if i + 1 < length triangle
then max (maxPath (i + 1) j) (maxPath (i + 1) (j + 1))
else 0)
triangle = [
[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, 9,70,98,73,93,38,53,60,04,23]]