55 lines
1.7 KiB
Haskell
55 lines
1.7 KiB
Haskell
-- main.hs as written by me, thuroughly fixed by <https://github.com/h7x4>
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main :: IO ()
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main = do
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file <- readFile "input.txt"
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let
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pairs :: [((Int, Int), (Int, Int))]
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pairs = inputLinesToPairs file
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putStrLn "Part 1: "
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print $ part1 pairs
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putStrLn "Part 2: "
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print $ part2 pairs
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-- Map each line of input from "1-2,3-4" to ((1,2),(3,4))
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inputLinesToPairs :: String -> [((Int, Int), (Int, Int))]
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inputLinesToPairs input = result
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where
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stringpairs :: [[String]]
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stringpairs = map (splitWhen (==',')) $ lines input
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parseRange :: String -> (Int, Int)
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parseRange pair = (read first, read second)
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where
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(first:second:_) = splitWhen (=='-') pair
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result :: [((Int, Int), (Int, Int))]
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result = map (\x -> (head x, last x)) $ map (map parseRange) stringpairs
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part1 :: [((Int, Int), (Int, Int))] -> Int
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part1 = length . filter (uncurry rangeIsContained)
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part2 :: [((Int, Int), (Int, Int))] -> Int
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part2 = length . filter (uncurry rangeOverlaps)
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-- True if any part of the two ranges overlap
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rangeOverlaps :: (Int, Int) -> (Int, Int) -> Bool
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rangeOverlaps (lo1, hi1) (lo2, hi2) = rangeIsContained (lo1, lo1) (lo2, hi2)
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|| (lo2 >= lo1 && lo2 <= hi1)
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|| (hi2 >= lo1 && hi2 <= hi1)
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-- True if the first range is entirely contained in the second range, or vice versa
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rangeIsContained :: (Int, Int) -> (Int, Int) -> Bool
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rangeIsContained (lo1, hi1) (lo2, hi2) = (lo1 <= lo2 && hi1 >= hi2)
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|| (lo1 >= lo2 && hi1 <= hi2)
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-- Modified from Prelude.words
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splitWhen :: (Char -> Bool) -> String -> [String]
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splitWhen p s = case dropWhile p s of
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"" -> []
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s' -> w : splitWhen p s''
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where (w, s'') = break p s'
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