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alisey/collatz.hs

Created May 17, 2014 14:13
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Longest Collatz Sequence (http://projecteuler.net/problem=14)
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collatz.hs
import Data.Bits
collatzLen :: Int -> Int -> Int
collatzLen len x
| x == 1 = len
| testBit x 0 = collatzLen (len + 2) (shiftR (3*x + 1) 1)
| otherwise = collatzLen (len + 1) (shiftR x 1)
main = print . snd . maximum $ [(collatzLen 0 x, x) | x <- [500000..1000000]]
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