Data commit

Task/EKG-sequence-convergence/Haskell/ekg-sequence-convergence.hs

@@ -0,0 +1,49 @@
+import Data.List (findIndex, isPrefixOf, tails)
+import Data.Maybe (fromJust)
+
+----------------------- EKG SEQUENCE ---------------------
+
+seqEKGRec :: Int -> Int -> [Int] -> [Int]
+seqEKGRec _ 0 l = l
+seqEKGRec k n [] = seqEKGRec k (n - 2) [k, 1]
+seqEKGRec k n l@(h : t) =
+  seqEKGRec
+    k
+    (pred n)
+    ( head
+        ( filter
+            (((&&) . flip notElem l) <*> ((1 <) . gcd h))
+            [2 ..]
+        ) :
+      l
+    )
+
+seqEKG :: Int -> Int -> [Int]
+seqEKG k n = reverse (seqEKGRec k n [])
+
+
+--------------------- CONVERGENCE TEST -------------------
+main :: IO ()
+main =
+  mapM_
+    ( \x ->
+        putStr "EKG ("
+          >> (putStr . show $ x)
+          >> putStr ") is "
+          >> print (seqEKG x 20)
+    )
+    [2, 5, 7, 9, 10]
+    >> putStr "EKG(5) and EKG(7) converge at "
+    >> print
+      ( succ $
+          fromJust $
+            findIndex
+              (isPrefixOf (replicate 20 True))
+              ( tails
+                  ( zipWith
+                      (==)
+                      (seqEKG 7 80)
+                      (seqEKG 5 80)
+                  )
+              )
+      )