Move History

Rooted by: Collatz sequence
Fork Selected
  • Sequences
    Arrays
    Data Types
    Code 
    module Collatz where

collatz :: Int -> [Int]
collatz = iterate next
  where next n | even n = n `div` 2
               | odd n = n * 3 + 1
     Test Cases 
    import Test.Hspec
import Collatz

main = hspec $ do
  describe "Collatz sequence" $ do
    it "One" $ do
      (take 5 $ collatz 1) `shouldBe` [1,4,2,1,4]
    it "Zero" $ do
      (take 3 $ collatz 0) `shouldBe` [0,0,0]
    it "Even" $ do
      (take 3 $ collatz 68) `shouldBe` [68,34,17]
    it "Odd" $ do
      (take 3 $ collatz 23) `shouldBe` [23,70,35]
    it "Cycle" $ do
      (take 6 $ collatz (-5)) `shouldBe` [-5,-14,-7,-20,-10,-5]
    it "Long" $ do
      (take 19 $ collatz 28) `shouldBe` [28,14,7,22,11,34,17,52,26,13,40,20,10,5,16,8,4,2,1]
    View Run Output
  • Code
    • module Collatz where
    • collatz :: Int -> [Int]
    • collatz n = n : collatz next
    • where next | even n = n `div` 2
    • | odd n = n * 3 + 1
    • collatz = iterate next
    • where next n | even n = n `div` 2
    • | odd n = n * 3 + 1