49 lines
1.6 KiB
Haskell
49 lines
1.6 KiB
Haskell
module Main where
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import Debug.Trace (trace)
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import System.Environment (getArgs)
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main :: IO ()
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main = do
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input <- readFile . head =<< getArgs
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print $ part1 input
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print $ part2 input
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part1 :: String -> Int
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part1 = length . filter (== 0) . scanl rotate 50 . map parse . lines
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rotate :: Integer -> Either Integer Integer -> Integer
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rotate pos (Left rot) = (pos - rot) `mod` 100
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rotate pos (Right rot) = (pos + rot) `mod` 100
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parse :: String -> Either Integer Integer
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parse ('L' : rest) = Left (read rest :: Integer)
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parse ('R' : rest) = Right (read rest :: Integer)
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parse s = error $ unwords [s, "is not on the form 'L$NUM' or 'R$NUM''"]
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test_input = "L68\nL30\nR48\nL5\nR60\nL55\nL1\nL99\nR14\nL82"
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part2 :: String -> Integer
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part2 = snd . head . reverse . scanl rotate2 (50, 0) . map parse . lines
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rotate2 :: (Integer, Integer) -> Either Integer Integer -> (Integer, Integer)
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rotate2 (pos, zeros) rot =
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let pos' = rotate pos rot
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newZeros = go pos rot
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in trace ("The dial is rotated " ++ show rot ++ " to point at " ++ show pos' ++ if newZeros > 0 then "; during this rotation it points to 0 " ++ (counting newZeros) else ".") (pos', zeros + newZeros)
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where
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counting :: Integer -> String
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counting 1 = "once"
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counting 2 = "twice"
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counting n = show n ++ " times"
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go :: Integer -> Either Integer Integer -> Integer
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go p (Left r)
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| p == r = 1
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| r > 100 = 1 + go p (Left (r - 100))
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| p /= 0 && p - r < 0 = 1 + go 0 (Left (r - p))
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| otherwise = 0
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go p (Right r) = (p + r) `div` 100
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between :: Integer -> (Integer, Integer) -> Bool
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between x (mn, mx) = x < mx && x > mn
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