Dinesman's multiple-dwelling problem: Difference between revisions

=={{header|Haskell}}==

The List monad is perfect for this kind of problem. One can express the problem statements in a very natural and concise way:

{{works with|GHC|6.10+}}

<lang haskell>import Data.List (permutations)

import Control.Monad (guard)

dinesman :: [(Int,Int,Int,Int,Int)]

dinesman = do

-- baker, cooper, fletcher, miller, smith are integers representing

-- the floor that each person lives on, from 1 to 5

-- Baker, Cooper, Fletcher, Miller, and Smith live on different floors

-- of an apartment house that contains only five floors.

[baker, cooper, fletcher, miller, smith] <- permutations [1..5]

-- Baker does not live on the top floor.

guard $ baker /= 5

-- Cooper does not live on the bottom floor.

guard $ cooper /= 1

-- Fletcher does not live on either the top or the bottom floor.

guard $ fletcher /= 5 && fletcher /= 1

-- Miller lives on a higher floor than does Cooper.

guard $ miller > cooper

-- Smith does not live on a floor adjacent to Fletcher's.

guard $ abs (smith - fletcher) /= 1

-- Fletcher does not live on a floor adjacent to Cooper's.

guard $ abs (fletcher - cooper) /= 1

-- Where does everyone live?

return (baker, cooper, fletcher, miller, smith)

main :: IO ()

main = do

print $ head dinesman -- print first solution: (3,2,4,5,1)

print dinesman -- print all solutions (only one): [(3,2,4,5,1)]</lang>