import ./Utils/Iters.cro

MaxBy gtr (It h tl) = MaxBy' gtr h (Iter tl)
MaxBy gtr h:tl = MaxBy' gtr h tl
MaxBy' gtr h tl = FoldIt (\h max -> if gtr h max then h else max) h tl

-- TODO: use a Dict to cache previous results
CollatzLen n = CollatzLen' n 1
CollatzLen' 1 len = len
CollatzLen' n len =
    CollatzLen' (if Even n then n / 2 else (3 * n + 1) / 2) (len + (if Even n then 1 else 2))

Main = Fst (MaxBy (\(a, l1) (b, l2) -> l1 > l2) (MapIt (\n -> (n, CollatzLen n)) (RangeIt 500000 1000000)))