57 lines
1.4 KiB
Idris
57 lines
1.4 KiB
Idris
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import System.File.ReadWrite
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import Data.String
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import Data.List
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data Item = I Char
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Eq Item where
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(I a) == (I b) = a == b
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Show Item where
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show (I a) = show a
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-- Define the priority of item
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priority : Item -> Int
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priority (I char) =
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if isUpper char then
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ord char - 38
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else
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ord char - 96
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-- Spiit a list in half
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splitHalf : List a -> Maybe (List a, List a)
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splitHalf list =
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let len : Int
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len = cast $ length list
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halfLen : Int
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halfLen = div len 2
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resultLen : Nat
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resultLen = cast halfLen
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in if len `mod` 2 == 0
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then Just (take resultLen list, drop resultLen list)
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else Nothing
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data Backpack = B (List Item) (List Item)
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-- Parse a backpack from a string
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parseBackpack : String -> Maybe Backpack
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parseBackpack input =
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let items = map I . unpack $ input
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in do (left, right) <- splitHalf items
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Just (B left right)
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-- Get the duplicated items
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duplicatedItems : Backpack -> List Item
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duplicatedItems (B left right) = nub $ intersect left right
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main : IO ()
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main =
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do file <- readFile "input"
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case file of
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Right content =>
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let backpacks = catMaybes . map parseBackpack . lines $ content
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priorityTotals = foldl (+) 0 . map (foldl (+) 0 . map priority . duplicatedItems) $ backpacks
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in do putStr "part 1: "
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printLn priorityTotals
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Left err => printLn err
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