day 22

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

src/Day22.hs

@@ -0,0 +1,46 @@
+module Main where
+
+import Data.Bits (Bits (xor))
+import qualified Data.Map as M
+
+type Bananas = M.Map Int Int
+
+evolve :: Int -> Int
+evolve =
+  (`mod` 16777216)
+    . (xor <*> (* 2048))
+    . (`mod` 16777216)
+    . (xor <*> (`div` 32))
+    . (`mod` 16777216)
+    . (xor <*> (* 64))
+
+part1 :: [Int] -> Int
+part1 = sum . map ((!! 2000) . iterate evolve)
+
+hash :: (Int, Int, Int, Int) -> Int
+hash (a, b, c, d) = a + 19 * (b + 19 * (c + 19 * d))
+
+bananas :: Bananas -> [Int] -> Bananas
+bananas f (a : b : c : d : e : xs) =
+  let key = hash (b - a, c - b, d - c, e - d)
+      next = bananas f (b : c : d : e : xs)
+   in case M.lookup key f of
+        Nothing -> M.insert key e next
+        Just _ -> next
+bananas f _ = f
+
+part2 :: [Int] -> Int
+part2 =
+  maximum
+    . M.elems
+    . M.unionsWith (+)
+    . map
+      (bananas M.empty . map (`mod` 10) . take 2001 . iterate evolve)
+
+main :: IO ()
+main =
+  do
+    buyers <- map read . words <$> readFile "./inputs/day22.in"
+
+    putStr "Part 1: " >> print (part1 buyers)
+    putStr "Part 2: " >> print (part2 buyers)