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Day 15 - strict recursive alternate solution that takes < 1 min

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Jonathan Chan 2017-12-15 00:43:08 -08:00
parent d378e3e50e
commit 906eb9106b
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15_strict.hs Normal file
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{-# LANGUAGE BangPatterns #-}
import Data.Function (on)
import Data.Bits ((.&.))
count :: Int -> (Int, Int) -> (Int, Int) -> (Int, Int) -> Int -> Int -> Int
count divisor (factorA, factorB) (seedA, seedB) (divA, divB) acc times =
if times == 0 then acc else
let !nextA = nextMaskBy factorA divA seedA
!nextB = nextMaskBy factorB divB seedB
!eq = fromEnum $ ((==) `on` (.&. 0xffff)) nextA nextB
in count divisor (factorA, factorB) (nextA, nextB) (divA, divB) (acc + eq) (times - 1)
where
nextMaskBy f d s = let t = (f * s) `mod` divisor in if (t .&. d) == 0 then t else nextMaskBy f d t
main :: IO ()
main = do
print $ count 2147483647 (16807, 48271) (634, 301) (0, 0) 0 40000000
print $ count 2147483647 (16807, 48271) (634, 301) (3, 7) 0 5000000