Euler Project Problem 577

counting-hexagons.hs

triangularNumbers = [ quot (x^2 + x) 2 | x <- [1..12345] ]

hexSums' :: Int -> [Int] -> [Int]
hexSums' n sumList =
  if allZeroes sumList then
    sumList
  else
    zipWith (+) sumList nextList
  where
    nextList = hexSums' (n+1) (take 12345 nextTriNums)
    nextTriNums = padding ++ map (*(n+1)) triangularNumbers
    padding  = replicate (n*3) 0

hexSums = hexSums' 1 triangularNumbers

hexes :: Int -> Int
hexes n = n

allZeroes :: [Int] -> Bool
allZeroes xs = and $ map (== 0) xs

main :: IO()
main = putStrLn $ show $ sum $ take 12343 hexSums