Sequences
Arrays
Data Types
Returns the Collatz sequence starting with the given number.
module Collatz where
collatz :: Int -> [Int]
collatz n = n : collatz next
where next | even n = n `div` 2
| odd n = n * 3 + 1import 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]