しりとり
30分プログラム、その55。
http://www.agusa.i.is.nagoya-u.ac.jp/person/mzp/hiki/?exerciseより。
与えられた単語を全て1回ずつ使い、しりとりができるかどうか判定するプログラムを書け。
*Main> siritori ["ABC","CBC","CDC"] [["ABC","CBC","CDC"],["ABC","CDC","CBC"]] *Main> siritori ["elvis","eve","alice","spaid"] [["alice","eve","elvis","spaid"]]
import Control.Monad connect :: String -> String -> Bool connect xs (y:ys) = (last xs) == y startFrom :: String->[String]->[[String]] startFrom start [x] | connect start x = [[x]] | otherwise = [] startFrom start choices = do choice <- choices guard $ connect start choice follow <- startFrom choice [x | x<-choices , x /= choice] return $ choice:follow siritori :: [String]->[[String]] siritori words = do word <- words follow <- startFrom word [x | x <- words, x /=word] return $ word:follow
