Euler14.hs

module Main where



euler14 =   max' [(length xs, n) | n<-[1..1000000], let xs = (collatz n)]
       where
         comp x y = if (fst x) > (fst y) then x else y 
         max'  = (foldr comp (0,0))


collatz n
        | n==1      = [1]
        | even n    = let m = n `div` 2 in n:(collatz m)
        | otherwise = let m = 3*n+1     in n:(collatz m)

main = print $ euler14