Euler Problem 14

euler_p14.hs

import Data.Word

collatzLen :: Int -> Word32 -> Int
collatzLen c 1 = c
collatzLen c n = collatzLen (c+1) $ if n `mod` 2 == 0 then n `div` 2 else 3*n+1

pmax x n = x `max` (collatzLen 1 n, n)

main = print . solve $ 1000000
    where solve xs = foldl pmax (1,1) [2..xs-1]

To compile:

ghc --make -O2 euler_p14.hs -fasm -o p14_fasm
ghc --make -O2 euler_p14.hs -fvia-C -o p14_viac

To run:

time ./p14_fasm
time ./p14_viac

You should probably use foldl' instead of foldl. Import it from Data.List.

p14_fasm    3.58s
p14_viac    0.84s

(same result with foldl' -- guess the strictness analyser does a good job for this one.)

great thanks a lot for this.