39 lines
1.2 KiB
Haskell
39 lines
1.2 KiB
Haskell
import Data.List
|
|
type YInt = Int
|
|
|
|
collatz :: YInt -> YInt
|
|
collatz n = if n<0 then 1 else if even n then n `quot` 2 else 3*n+1
|
|
|
|
-- The l `seq` is necessary to not be lazy (non-strict)
|
|
-- And not to fill the stack
|
|
lencollatz' :: YInt -> YInt -> YInt
|
|
lencollatz' l 1 = l
|
|
lencollatz' l n = l `seq` lencollatz' (l+1) (collatz n)
|
|
|
|
lencollatz = lencollatz' 0
|
|
|
|
-- The j `seq` is necessary to not be lazy (non-strict)
|
|
-- And not to fill the stack
|
|
maximalIndex :: (YInt,YInt) -> YInt -> [YInt] -> (YInt,YInt)
|
|
maximalIndex (m,i) j [] = (m,i)
|
|
maximalIndex (m,i) j (x:xs) = j `seq` maximalIndex res (j+1) xs
|
|
where res = if x>m then (x,j) else (m,i)
|
|
|
|
showCollatz :: YInt -> String
|
|
showCollatz 1 = "1"
|
|
showCollatz n = show n ++ " → " ++ showCollatz ( collatz n )
|
|
|
|
pure (Just x) = x
|
|
|
|
main = do
|
|
putStrLn $ "max len: " ++ show m
|
|
putStrLn $ "max value: " ++ show i
|
|
-- print mrec
|
|
-- print irec
|
|
-- putStrLn $ showCollatz $ toInteger i
|
|
where
|
|
array = map lencollatz [1..1000000]
|
|
m = maximum array
|
|
i = 1 + pure (elemIndex m array)
|
|
(mrec,irec) = maximalIndex (0,0) 1 array
|
|
|