tasks a-s

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

@@ -0,0 +1,13 @@
+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]

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

@@ -0,0 +1,12 @@
+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]

Task/Ordered-Partitions/Haskell/ordered-partitions-3.hs

@@ -0,0 +1,15 @@
+-- choose m out of n items, return tuple of chosen and the rest
+choose aa _ 0 = [([], aa)]
+choose aa@(a:as) n m
+	| n == m = [(aa, [])]
+	| otherwise =	map (\(x,y) -> (a:x, y)) (choose as (n-1) (m-1)) ++
+			map (\(x,y) -> (x, a:y)) (choose as (n-1) m)
+
+partitions x = combos [1..n] n x where
+	n = sum x
+	combos _ _ [] = [[]]
+	combos s n (x:xs) = [ l : r |	(l,rest) <- choose s n x,
+					r <- combos rest (n - x) xs]
+
+
+main = mapM_ print $ partitions [5,5,5]