Sha256: 8ea703833850a4afcc49b927640aae26c8cdd7ab395227a528d47a35fffc91bc
Contents?: true
Size: 703 Bytes
Versions: 381
Compression:
Stored size: 703 Bytes
Contents
module Dominoes (chain) where
import Data.List (delete)
import Data.Maybe (listToMaybe, mapMaybe)
chain :: [(Int, Int)] -> Maybe [(Int, Int)]
chain [] = Just []
chain (x@(left, right):xs) = fmap (x:) (subchain xs left right)
subchain :: [(Int, Int)] -> Int -> Int -> Maybe [(Int, Int)]
subchain [] chainLeft chainRight = if chainLeft == chainRight then Just [] else Nothing
subchain l chainLeft chainRight = listToMaybe (mapMaybe subchain' l)
where subchain' (a, b) | a == chainRight = fmap ((a, b):) (subchain (delete (a, b) l) chainLeft b)
subchain' (a, b) | b == chainRight = fmap ((b, a):) (subchain (delete (a, b) l) chainLeft a)
subchain' _ = Nothing
Version data entries
381 entries across 381 versions & 1 rubygems