p018.hs

import Data.List

--triangle = [[3],[7,4],[2,4,6],[8,5,9,3]]

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]
    , [04,62,98,27,23,09,70,98,73,93,38,53,60,04,23]
    ]

tuplePair :: [a] -> [(a,a)]
tuplePair (x:[]) = [(x,x)]
tuplePair (x:y:xs) = (x,y) : tuplePair (y:xs)

pickOption :: Int -> (Int, Int) -> Int
pickOption x options = maximum [first, second]
    where first  = x + (fst options)
          second = x + (snd options)

process :: [[Int]] -> [Int]
process (x:[])   = x
process (x:y:xs) = process (calcRow : xs)
    where expandedRow = tuplePair $ (head x) : x
          calcRow     = zipWith pickOption y expandedRow

main = print $ maximum $ process triangle