day 22

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

aoc2024.cabal

@@ -164,3 +164,9 @@ executable day21
   hs-source-dirs: src
   main-is:        Day21.hs
   build-depends:  containers
+
+executable day22
+  import:         common
+  hs-source-dirs: src
+  main-is:        Day22.hs
+  build-depends:  containers

fetch.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+SOURCE_DIR=$(realpath "$(dirname "$0")")
+INPUT_DIR=${INPUT_DIR:="$SOURCE_DIR/inputs"}
+
+help () {
+  echo "usage:   $0 <day1-day25>"
+  echo "example: $0 day15"
+  echo "         $0 15"
+  echo "         $0 all"
+}
+
+fetch () {
+  TMPFILE=$(mktemp)
+  curl "https://adventofcode.com/2024/day/${1}/input"          \
+    -s --fail-with-body --cookie "session=$AOC_SESSION"            \
+    -o "${TMPFILE}"
+
+  mkdir -p "$INPUT_DIR"
+  mv "$TMPFILE" "$INPUT_DIR/day${1}.in"
+  echo "Fetched Day $1"
+}
+
+if [[ $# != 1 || ! "${1#day}" =~ ^([1-9]|1[0-9]|2[0-5]|all)$ ]]; then
+  help
+  exit 1
+fi
+
+if [[ -z "${AOC_SESSION}" ]]; then
+  echo "\$AOC_SESSION is not set"
+  exit 1
+fi
+
+if [[ $1 == "all" ]]; then
+    for x in {1..25}; do fetch "$x"; done
+else
+    fetch "${1#day}"
+fi

flake.nix

@@ -31,7 +31,7 @@
           let
             name = n: "day${(if n < 10 then "0" else "" ) + toString n}";
           in
-          with pkgs.lib; genAttrs (map name (range 1 21))
+          with pkgs.lib; genAttrs (map name (range 1 22))
             (n: {
               type = "app";
               program = "${self'.packages.aoc2024}/bin/${n}";

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)