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{-
- Solution to Project Euler problem 11
- Copyright (c) Project Nayuki. All rights reserved.
-
- https://www.nayuki.io/page/project-euler-solutions
- https://github.com/nayuki/Project-Euler-solutions
-}
main = putStrLn (show ans)
ans = foldl1 max (concat [
lineProducts 1 0 4,
lineProducts 0 1 4,
lineProducts 1 1 4,
lineProducts 1 (-1) 4])
lineProducts dx dy n = [product [square !! (y + i * dy) !! (x + i * dx) | i <- [0 .. n - 1]]
| y <- [0 .. (length square) - 1], x <- [0 .. (length (square !! y)) - 1],
inBounds (x + (n - 1) * dx) (y + (n - 1) * dy)]
inBounds x y = y >= 0 && y < (length square) && x >= 0 && x < (length (square !! y))
square =
[[ 8,02,22,97,38,15,00,40,00,75,04,05,07,78,52,12,50,77,91, 8],
[49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,04,56,62,00],
[81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,03,49,13,36,65],
[52,70,95,23,04,60,11,42,69,24,68,56,01,32,56,71,37,02,36,91],
[22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80],
[24,47,32,60,99,03,45,02,44,75,33,53,78,36,84,20,35,17,12,50],
[32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70],
[67,26,20,68,02,62,12,20,95,63,94,39,63, 8,40,91,66,49,94,21],
[24,55,58,05,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72],
[21,36,23, 9,75,00,76,44,20,45,35,14,00,61,33,97,34,31,33,95],
[78,17,53,28,22,75,31,67,15,94,03,80,04,62,16,14, 9,53,56,92],
[16,39,05,42,96,35,31,47,55,58,88,24,00,17,54,24,36,29,85,57],
[86,56,00,48,35,71,89,07,05,44,44,37,44,60,21,58,51,54,17,58],
[19,80,81,68,05,94,47,69,28,73,92,13,86,52,17,77,04,89,55,40],
[04,52, 8,83,97,35,99,16,07,97,57,32,16,26,26,79,33,27,98,66],
[88,36,68,87,57,62,20,72,03,46,33,67,46,55,12,32,63,93,53,69],
[04,42,16,73,38,25,39,11,24,94,72,18, 8,46,29,32,40,62,76,36],
[20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,04,36,16],
[20,73,35,29,78,31,90,01,74,31,49,71,48,86,81,16,23,57,05,54],
[01,70,54,71,83,51,54,69,16,92,33,48,61,43,52,01,89,19,67,48]]