-- Soluciones alternativas; estudiar a conciencia
--
-- import List
--
-- grid = ...
--
-- myMaximum [] = 0
-- myMaximum xs = maximum xs
--
-- takeBy n = filter ((n==) . length) . map (take n) . tails
--
-- maxBy n = myMaximum . map product . takeBy n
--
-- maxInRows n = maximum . map (maxBy n)
--
-- maxInCols n = maxInRows n . transpose
--
-- maxInLR n = maxInRows n . transpose . zipWith drop [0..]
--
-- maxInRL n = maxInLR n . map reverse
--
-- main = print $ maximum $ map (flip ($ 4) grid) [maxInRows, maxInCols, maxInLR, maxInRL]
-------------------------------------------------------------------------------------------
-- import Data.Array
-- import Data.List
--
-- input = unlines $
--         [ "08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08",
--           "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 08 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 09 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 09 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 08 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 08 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"]
--
-- n = 20
--
-- mbounds = ((1,1), (n,n))
--
-- matrix :: Array (Int, Int) Int
-- matrix = listArray mbounds $ map read $ words input
--
-- k = 4
--
-- -- right, down, right-diag, left-diag
-- directions = [ (0,1), (1,0), (1,1), (1,-1) ]
--
-- move (x,y) (dx,dy) = (x+dx, y+dy)
--
-- solution = maximum [ product (takeLine pt dir) |
--                      pt  <- range mbounds,
--                      dir <- directions]
--     where takeLine pt dir = [ matrix!pt' |
--                               pt' <- take k $ iterate (move dir) pt,
--                               inRange mbounds pt' ]

import Data.List (transpose)

grid :: [[Int]]
grid =
	[[08, 02, 22, 97, 38, 15, 00, 40, 00, 75, 04, 05, 07, 78, 52, 12, 50, 77, 91, 08]
	,[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, 08, 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, 09, 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, 09, 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, 08, 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, 08, 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]]

max4 :: [Int] -> Int
max4 v
	| (length v) < 4	= 0
	| otherwise			= maximum [product $ take 4 v, max4 $ tail v]

horizontal :: [[Int]] -> Int
horizontal = horizontal'
	where
		horizontal' :: [[Int]] -> Int
		horizontal' [] = 0
		horizontal' (v:m) = maximum [(max4 v), (horizontal' m)]

vertical :: [[Int]] -> Int
vertical = horizontal . transpose

diagonal :: [[Int]] -> Int
diagonal m = maximum (map (max4 . diag) [0..(len-1)])
	where
		diag n = [grid !! x !! y | x <- [0..n], y <- [0..n], x+y == n]
		len = length grid

diagonal_back :: [[Int]] -> Int
diagonal_back = diagonal . (map reverse)

p11 :: Int
p11 = maximum $ [horizontal grid, vertical grid, diagonal grid, diagonal_back grid]

main = putStrLn $ "Solution: " ++ show p11