52 lines
1.2 KiB
Haskell
52 lines
1.2 KiB
Haskell
module Aoc.Day4 (solve) where
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import Aoc (runReadP)
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import Data.Char
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import Text.ParserCombinators.ReadP
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type Range = (Int, Int)
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type Row = (Range, Range)
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type Input = [Row]
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parse :: String -> Input
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parse = map (runReadP rowP) . lines
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where
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intP :: ReadP Int
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intP = do
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digits <- munch1 isDigit
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return $ read digits
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rangeP :: ReadP Range
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rangeP = do
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l <- intP
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_ <- char '-'
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r <- intP
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return (l, r)
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rowP :: ReadP Row
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rowP = do
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a <- rangeP
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_ <- char ','
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b <- rangeP
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return (a, b)
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fullOverlap :: Row -> Bool
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fullOverlap ((a, b), (c, d))
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| a <= c && b >= d = True
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| c <= a && d >= b = True
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| otherwise = False
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overlap :: Row -> Bool
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overlap ((a, b), (c, d))
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| b < c = False -- first is fully to the left of second
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| d < a = False -- first is fully to the right of second
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| otherwise = True -- there's some overlap
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solve' :: String -> (Row -> Bool) -> Integer
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solve' input predicate = fromIntegral $ length $ filter predicate $ parse input
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solve :: Integer -> String -> String
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solve 1 input = show $ solve' input fullOverlap
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solve 2 input = show $ solve' input overlap
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solve _ _ = "?"
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