tasks a-s

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]