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-rw-r--r--2020/23-Crab_Cups/example1
-rw-r--r--2020/23-Crab_Cups/first.hs66
-rw-r--r--2020/23-Crab_Cups/input1
3 files changed, 68 insertions, 0 deletions
diff --git a/2020/23-Crab_Cups/example b/2020/23-Crab_Cups/example
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diff --git a/2020/23-Crab_Cups/first.hs b/2020/23-Crab_Cups/first.hs
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+-- requires cabal install --lib megaparsec parser-combinators
+module Main (main) where
+import Control.Monad (void, when)
+import Data.List qualified as L
+import Data.Map qualified as M
+import Data.Maybe (fromJust)
+import Data.Set qualified as S
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import System.Exit (die)
+
+exampleExpectedOutput = 67384529
+
+type Cup = Int
+type Input = [Cup]
+type History = [Input]
+
+type Parser = Parsec Void String
+
+parseCup :: Parser Cup
+parseCup = do
+ n <- digitChar
+ return $ read [n] - 1 -- so that there is a 0 in there and then we can use modulo
+
+parseInput' :: Parser Input
+parseInput' = some parseCup <* optional (char '\n') <* eof
+
+parseInput :: String -> IO Input
+parseInput filename = do
+ input <- readFile filename
+ case runParser parseInput' filename input of
+ Left bundle -> die $ errorBundlePretty bundle
+ Right input' -> return input'
+
+score :: Input -> Int
+score (0:xs) = read . concat $ map (\i -> show (i+1)) xs
+score (x:xs) = score $ xs ++ [x]
+
+compute' :: Input -> Int -> Int
+compute' input 0 = score input
+compute' (current:one:two:three:xs) remainingMoves = compute' step (remainingMoves - 1)
+ where
+ l = length xs + 4
+ destinationIndex :: Int
+ destinationIndex = case L.elemIndex ((current - 1) `mod` l) xs of
+ Just i -> i
+ Nothing -> case L.elemIndex ((current - 2) `mod` l) xs of
+ Just i -> i
+ Nothing -> case L.elemIndex ((current - 3) `mod` l) xs of
+ Just i -> i
+ Nothing -> fromJust $ L.elemIndex ((current - 4) `mod` l) xs
+ destinationIndex' = destinationIndex + 1
+ step :: Input
+ step = concat [take destinationIndex' xs, [one, two, three], drop destinationIndex' xs, [current]]
+
+compute :: Input -> Int
+compute input = compute' input 100
+
+main :: IO ()
+main = do
+ example <- parseInput "example"
+ let exampleOutput = compute example
+ when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+ input <- parseInput "input"
+ print $ compute input
diff --git a/2020/23-Crab_Cups/input b/2020/23-Crab_Cups/input
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+963275481