Haskell/Permutation: Add

Author: GHScan

Haskell/Permutation/main.hs

@@ -0,0 +1,18 @@
+import Data.List
+main = putStrLn $ show output
+output = length$permutation2 "123456789"
+
+permutation l@[x] = [l]
+permutation l@(h:t) = [_insert i sub|i<-[0..length l - 1],sub<-permutation t]
+    where 
+    _insert i sub = left ++ h:right
+        where
+        (left,right) = splitAt i sub
+
+permutation2 l@[x] = [l]
+permutation2 l = concat [_use i|i<-[1..length l]]
+    where 
+    _use i = map (_head:) $permutation2 _tail
+        where
+        _head = l !! (i - 1)
+        _tail = (init $take i l) ++ drop i l