eldridge.cam
Advent of Code solutions
1import Control.Arrow
2import Data.Bits
3import Data.List
4import qualified Data.Map.Strict as Map
5
6prng :: Int -> Int
7prng =
8 id &&& (* 64)
9 >>> uncurry xor
10 >>> (`mod` 16777216)
11 >>> (id &&& (`div` 32))
12 >>> uncurry xor
13 >>> (`mod` 16777216)
14 >>> (id &&& (* 2048))
15 >>> uncurry xor
16 >>> (`mod` 16777216)
17
18prices rngs@(a : b : c : d : e : _) = Map.singleton (b - a, c - b, d - c, e - d) e : prices (drop 1 rngs)
19prices _ = []
20
21answer = maximum . Map.unionsWith (+) . fmap (Map.unions . prices . fmap (`mod` 10) . take 2000 . iterate prng . read) . lines
22
23main = getContents >>= print . answer