RosettaCodeData/Task/Ordered-Partitions/Haskell/ordered-partitions-2.hs

13 lines
399 B
Haskell

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