September Morn Update

Task/Stern-Brocot-sequence/Haskell/stern-brocot-sequence-2.hs

@@ -0,0 +1,20 @@
+import Data.List (nubBy, sortBy)
+import Data.Ord (comparing)
+import Data.Monoid ((<>))
+import Data.Function (on)
+
+sternBrocot :: [Int]
+sternBrocot =
+  let go (a:b:xs) = (b : xs) <> [a + b, b]
+  in head <$> iterate go [1, 1]
+
+-- TEST -------------------------------------------------------------
+main :: IO ()
+main = do
+  print $ take 15 sternBrocot
+  print $
+    take 10 $
+    nubBy (on (==) fst) $
+    sortBy (comparing fst) $ takeWhile ((110 >=) . fst) $ zip sternBrocot [1 ..]
+  print $ take 1 $ dropWhile ((100 /=) . fst) $ zip sternBrocot [1 ..]
+  print $ (all ((1 ==) . uncurry gcd) . (zip <*> tail)) $ take 1000 sternBrocot