Initial commit

2017/15/day15.hs

@@ -0,0 +1,29 @@
+#!/usr/bin/env stack
+-- stack --resolver lts-9.18 script
+
+import Data.Bits
+import Data.List
+
+genA :: Integral a => a -> a
+genA n = (16807 * n) `rem` 2147483647
+
+genB :: Integral a => a -> a
+genB n = (48271 * n) `rem` 2147483647
+
+matchLowest16Bits :: (Bits a, Num a) => a -> a -> Bool
+matchLowest16Bits n1 n2 =
+  n1 .&. 0xFFFF == n2 .&. 0xFFFF
+
+main :: IO ()
+main = do
+  let (inputA, inputB) = (783, 325) :: (Int, Int)
+  let n = 40000000
+  let seqA = take n $ iterate genA inputA
+  let seqB = take n $ iterate genB inputB
+  print . foldl' (flip ((+) . fromEnum)) 0 $ zipWith matchLowest16Bits seqA seqB
+  let n' = 5000000
+  let seqA' = take n' . filter (\k -> k `rem` 4 == 0)
+              $ iterate genA inputA
+  let seqB' = take n' . filter (\k -> k `rem` 8 == 0)
+              $ iterate genB inputB
+  print . foldl' (flip ((+) . fromEnum)) 0 $ zipWith matchLowest16Bits seqA' seqB'