Euler_18.hs

main :: IO ()
main = print $ maximum_path_sum [[75],[95,64],[17,47,82],[18,35,87,10],[20,4,82,47,65],[19,1,23,75,3,34],[88,2,77,73,7,63,67],[99,65,4,28,6,16,70,92],[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],[63,66,4,68,89,53,67,30,73,16,69,87,40,31],[4,62,98,27,23,9,70,98,73,93,38,53,60,4,23]]
 
maximum_path_sum :: [[Int]] -> Int
maximum_path_sum = sum . (maximum_path [] (0,0))
 
maximum_path :: [Int] -> (Int,Int) -> [[Int]] -> [Int]
maximum_path acc i@(x,y) paths
	| x == (length paths)-1 = acc'
	| otherwise = maximum_path acc' i' paths
	where 	acc' = (paths !! x !! y):acc
		i' = (next_coordinates i paths)
 
next_coordinates :: (Int,Int) -> [[Int]] -> (Int,Int)
next_coordinates coord mat 
	| below >= below_next 	= (i+1,j)
	| otherwise 		= (i+1,j+1) 
	where 	below = (mat !! (i+1) !! j)
		below_next = (mat !! (i+1) !! (j+1))
		i = fst coord
		j = snd coord