import Data.List
import Data.Ord
import qualified Data.MemoCombinators as Memo

collatzLength :: Int -> Int
collatzLength = Memo.arrayRange (1, 1000000) collatzLength'
  where
    collatzLength' 1 = 1
    collatzLength' n | odd n  = 1 + collatzLength (3 * n + 1)
                     | even n = 1 + collatzLength (n `quot` 2)

main = print $ maximumBy (comparing fst) $ [(collatzLength n, n) | n <- [1..1000000]]

euler14.o: In function `s1pw_info':
(.text+0x8dd): undefined reference to `__stginit_datazmmemocombinatorszm0zi4zi1_DataziMemoCombinators_'
euler14.o: In function `rfX_info':
(.text+0x35d): undefined reference to `datazmmemocombinatorszm0zi4zi1_DataziMemoCombinators_arrayRange_info'
euler14.o: In function `rfX_srt':
(.data+0x4c): undefined reference to `datazmmemocombinatorszm0zi4zi1_DataziMemoCombinators_arrayRange_closure'
collect2: ld returned 1 exit status