commit 7aae97acb787395c98af60adb6f7df2e3824e945 · drubery.com/aoc2025

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src/Day9.hs

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       module Day9 where

     

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       part1 :: String -> String

     

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       part1 _ = "Day 9 part 1"

     

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       part2 :: String -> String

     

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       part2 _ = "Day 9 part 2"

     

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       module Day9 where

     

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       import Util

     

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       parseLine :: [String] -> Point2

     

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       parseLine [x,y] = (read x, read y)

     

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       parse :: String -> [Point2]

     

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       parse s = map (parseLine . split ',') $ lines s

     

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       area :: Point2 -> Point2 -> Int

     

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       area (x,y) (z,w) = (abs (x - z) + 1) * (abs (y - w) + 1)

     

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       part1 :: String -> String

     

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       part1 input =

     

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         let pts = parse input

     

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          in show $

     

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             maximum $

     

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             [ area p q | p <- pts, q <- pts ]

     

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       uniq :: Eq a => [a] -> [a]

     

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       uniq [] = []

     

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       uniq [a] = [a]

     

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       uniq (a:b:cs) = if a == b then uniq (b:cs) else a : (uniq (b:cs))

     

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       edgeIntersect :: (Point2, Point2) -> (Point2, Point2) -> Bool

     

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       edgeIntersect (p,q) (r,s) =

     

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         max (fst r) (fst s) > min (fst p) (fst q) &&

     

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         min (fst r) (fst s) < max (fst p) (fst q) &&

     

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         max (snd r) (snd s) > min (snd p) (snd q) &&

     

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         min (snd r) (snd s) < max (snd p) (snd q)

     

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       containsRect :: Point2 -> Point2 -> [(Point2,Point2)] -> Bool

     

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       containsRect p q edges =

     

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         not $ or [edgeIntersect (p,q) e | e <- edges]

     

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       part2 :: String -> String

     

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       part2 input =

     

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         let pts = parse input

     

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             edges = zip pts ((tail pts) ++ [head pts])

     

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          in show $

     

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             maximum $

     

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             [area p q | p <- pts, q <- pts, containsRect p q edges]