commit 68a28aeba614f4c417ac8aa311ed4bcdd70f552f · drubery.com/aoc2025

+42 -2
src/Day2.hs
···

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       module Day2 where

     

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       import Debug.Trace

     

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       split :: Char -> String -> [String]

     

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       split c s = case dropWhile (== c) s of

     

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                     "" -> []

     

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                     s' -> w : split c s''

     

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                           where (w, s'') = break (== c) s'

     

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       isPartOneCandidate :: Int -> Bool

     

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       isPartOneCandidate n =

     

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         let s = show n

     

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             d = length s

     

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          in take (d `div` 2) s == drop (d `div` 2) s

     

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       isPartTwoCandidate :: Int -> Bool

     

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       isPartTwoCandidate n =

     

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         let s = show n

     

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             d = length s

     

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             cands = [concat $ replicate k $ take (d `div` k) s | k <- [2..d]]

     

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          in any (== s) cands

     

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       parseEntry :: [String] -> (Int, Int)

     

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       parseEntry (a : b : _) = (read a, read b)

     

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       parseEntry _ = error "Unreachable "

     

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       parse :: String -> [(Int, Int)]

     

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       parse s = 

     

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           map (parseEntry . split '-') $

     

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           split ',' s

     

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       part1 :: String -> String

     

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       part1 _ = "Day 2 part 1"

     

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       part1 input = show $

     

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           sum $

     

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           filter isPartOneCandidate $

     

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           concat $

     

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           map (\(a,b) -> [a..b]) $

     

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           parse input

     

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       part2 :: String -> String

     

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       part2 _ = "Day 2 part 2"

     

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       part2 input = show $

     

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           sum $

     

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           filter isPartTwoCandidate $

     

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           concat $

     

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           map (\(a,b) -> [a..b]) $

     

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           parse input