RosettaCodeData/Task/Ordered-Partitions/Haskell/ordered-partitions-1.hs

14 lines
353 B
Haskell

import Data.List ((\\))
comb :: Int -> [a] -> [[a]]
comb 0 _ = [[]]
comb _ [] = []
comb k (x:xs) = map (x:) (comb (k-1) xs) ++ comb k xs
partitions :: [Int] -> [[[Int]]]
partitions xs = p [1..sum xs] xs
where p _ [] = [[]]
p xs (k:ks) = [ cs:rs | cs <- comb k xs, rs <- p (xs \\ cs) ks ]
main = print $ partitions [2,0,2]