55 lines
1.6 KiB
Haskell
55 lines
1.6 KiB
Haskell
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import Data.Char
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main = do
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let list = []
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file <- readFile "input.txt"
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let inputLines = lines file
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let stringpairs = map (splitWhen (==',')) inputLines
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let listpairs = map (map parseRange) stringpairs
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let pairs = map (\x -> (head x, last x)) listpairs
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-- Each line of input has now gone from "1-2,3-4" to ((1,2),(3,4))
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let containedWithin = map (uncurry rangeIsContained) pairs
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let containedCount = length $ filter (==True) containedWithin
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print "Part 1: "
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print containedCount
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let overlap = map (uncurry rangeOverlaps) pairs
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let overlapCount = length $ filter (==True) overlap
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print "Part 2: "
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print overlapCount
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-- "1-3" -> (1,3)
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parseRange :: String -> (Int, Int)
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parseRange pair = do
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let numbers = splitWhen (=='-') pair
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let first = read (numbers !! 0) :: Int
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let second = read (numbers !! 1) :: Int
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(first, second)
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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)
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| lo1 <= lo2 && hi1 >= hi2 = True
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| lo1 >= lo2 && hi1 <= hi2 = True
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| otherwise = False
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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)
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| rangeIsContained (lo1, lo1) (lo2, hi2) = True
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| lo2 >= lo1 && lo2 <= hi1 = True
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| hi2 >= lo1 && hi2 <= hi1 = True
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| otherwise = False
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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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