Initial data commit

Task/Recamans-sequence/Haskell/recamans-sequence-2.hs

@@ -0,0 +1,42 @@
+import Data.Set (Set, fromList, insert, isSubsetOf, member, size)
+import Data.Bool (bool)
+
+firstNRecamans :: Int -> [Int]
+firstNRecamans n = reverse $ recamanUpto (\(_, i, _) -> n == i)
+
+firstDuplicateR :: Int
+firstDuplicateR = head $ recamanUpto (\(rs, _, set) -> size set /= length rs)
+
+recamanSuperset :: Set Int -> [Int]
+recamanSuperset setInts =
+  tail $ recamanUpto (\(_, _, setR) -> isSubsetOf setInts setR)
+
+recamanUpto :: (([Int], Int, Set Int) -> Bool) -> [Int]
+recamanUpto p = rs
+  where
+    (rs, _, _) =
+      until
+        p
+        (\(rs@(r:_), i, seen) ->
+            let n = nextR seen i r
+            in (n : rs, succ i, insert n seen))
+        ([0], 1, fromList [0])
+
+nextR :: Set Int -> Int -> Int -> Int
+nextR seen i r =
+  let back = r - i
+  in bool back (r + i) (0 > back || member back seen)
+
+-- TEST ---------------------------------------------------------------
+main :: IO ()
+main =
+  (putStrLn . unlines)
+    [ "First 15 Recamans:"
+    , show $ firstNRecamans 15
+    , []
+    , "First duplicated Recaman:"
+    , show firstDuplicateR
+    , []
+    , "Length of Recaman series required to include [0..1000]:"
+    , (show . length . recamanSuperset) $ fromList [0 .. 1000]
+    ]