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  1. Prepare
  2. Algorithms
  3. Bit Manipulation
  4. Xor-sequence
  5. Discussions

Xor-sequence

  • jmcparland
     + 0 comments

    Haskell

    So, if you look at the sequence of running XORs over the XORs, there's a pattern. I didn't give it much thought after that -- just implement the lookup function.

    module Main where

import Control.Monad (replicateM_)
import Data.Bits (xor)

lu :: Int -> Integer
lu 0 = 1
lu 1 = 2
lu 2 = 2
lu x = do
    let (q, r) = (x - 3) `quotRem` 8
        b = 8 * (fromIntegral q) + 6 :: Integer
     in [b, b + 1, 0, 0, b + 2, b + 3, 2, 2] !! r

solve :: Int -> Int -> Integer
solve 1 b = lu (b - 1)
solve a b = xor (lu (a - 2)) (lu (b - 1))

main :: IO ()
main = do
    cases <- readLn
    replicateM_ cases $ do
        [a, b] <- map read . words <$> getLine
        print $ solve a b