82 lines
2.2 KiB
Agda
82 lines
2.2 KiB
Agda
module Day4
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import Prelude
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import Node
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import Aoc
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data Problem : U where
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P : Int → String → Problem
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get : Problem → Int → Int → Char
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get (P size text) r c =
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if r < 0 || size <= r then '.'
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else if c < 0 || size <= c then '.'
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else sindex text (r * (size + 1) + c)
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check : Problem → Int → Int → Int × Int → Int
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check prob r c (dr,dc) =
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if (get prob r c) /= 'X' then 0
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else if (get prob (r + dr) (c + dc)) /= 'M' then 0
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else if (get prob (r + 2 * dr) (c + 2 * dc)) /= 'A' then 0
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else if (get prob (r + 3 * dr) (c + 3 * dc)) /= 'S' then 0
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else 1
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tail : ∀ a. List a → List a
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tail Nil = Nil
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tail (x :: xs) = xs
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dirs : List (Int × Int)
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dirs = tail $ _,_ <$> (0 :: 0 - 1 :: 1 :: Nil) <*> (0 :: 0 - 1 :: 1 :: Nil)
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part1 : Problem → Int
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part1 (P size text) = go 0 0 0
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where
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go : Int → Int → Int → Int
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go acc r c =
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if r == size then acc else
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if c == size then go acc (r + 1) 0 else
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let acc = foldl _+_ acc $ map (check (P size text) r c) dirs in
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go acc r (c + 1)
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pats : List (Char × Char × Char × Char)
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pats = ('M', 'M', 'S', 'S') ::
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('S', 'M', 'M', 'S') ::
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('S', 'S', 'M', 'M') ::
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('M', 'S', 'S', 'M') ::
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Nil
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check2 : Problem → Int → Int → (Char × Char × Char × Char) → Int
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check2 prob r c (w,x,y,z) =
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if (get prob r c) /= 'A' then 0
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else if (get prob (r - 1) (c - 1)) /= w then 0
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else if (get prob (r - 1) (c + 1)) /= x then 0
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else if (get prob (r + 1) (c + 1)) /= y then 0
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else if (get prob (r + 1) (c - 1)) /= z then 0
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else 1
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part2 : Problem → Int
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part2 (P size text) = go 0 0 0
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where
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go : Int → Int → Int → Int
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go acc r c =
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if r == size then acc else
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if c == size then go acc (r + 1) 0 else
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let acc = foldl _+_ acc $ map (check2 (P size text) r c) pats in
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go acc r (c + 1)
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run : String -> IO Unit
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run fn = do
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putStrLn fn
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text <- readFile fn
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let lines = split (trim text) "\n"
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-- I'm going to assume it's square for convenience
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-- part2 will probably wrap around.
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let size = length lines
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printLn $ "part1 " ++ show (part1 $ P (cast size) text)
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printLn $ "part2 " ++ show (part2 $ P (cast size) text)
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main : IO Unit
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main = do
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run "aoc2024/day4/eg.txt"
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run "aoc2024/day4/input.txt"
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