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-rw-r--r--2020/25-Combo_Breaker/example2
-rw-r--r--2020/25-Combo_Breaker/first.hs57
-rw-r--r--2020/25-Combo_Breaker/input2
3 files changed, 61 insertions, 0 deletions
diff --git a/2020/25-Combo_Breaker/example b/2020/25-Combo_Breaker/example
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+++ b/2020/25-Combo_Breaker/example
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+5764801
+17807724
diff --git a/2020/25-Combo_Breaker/first.hs b/2020/25-Combo_Breaker/first.hs
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+++ b/2020/25-Combo_Breaker/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 Math.NumberTheory.Powers.Modular
+import Text.Megaparsec
+import Text.Megaparsec.Char
+import System.Exit (die)
+
+exampleExpectedOutput = 14897079
+
+type Input = (Integer, Integer)
+
+type Parser = Parsec Void String
+
+parseInteger :: Parser Integer
+parseInteger = do
+ n <- some digitChar
+ void $ optional (char '\n')
+ return $ read n
+
+parseInput' :: Parser Input
+parseInput' = do
+ a <- parseInteger
+ b <- parseInteger
+ void eof
+ return (a, b)
+
+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'
+
+transform :: Integer -> Int -> Integer
+transform subjectNum loopSize = powMod subjectNum loopSize 20201227
+
+compute :: Input -> Integer
+compute (cardPubKey, doorPubKey) = encryptionKey
+ where
+ cardLoopSize = fromJust . L.elemIndex cardPubKey $ map (transform 7) [0..]
+ doorLoopSize = fromJust . L.elemIndex doorPubKey $ map (transform 7) [0..]
+ encryptionKey = transform doorPubKey cardLoopSize
+
+main :: IO ()
+main = do
+ example <- parseInput "example"
+ let exampleOutput = compute example
+ when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+ print "OK"
+ input <- parseInput "input"
+ print $ compute input
diff --git a/2020/25-Combo_Breaker/input b/2020/25-Combo_Breaker/input
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+++ b/2020/25-Combo_Breaker/input
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+17773298
+15530095