54 lines
1.1 KiB
Idris
54 lines
1.1 KiB
Idris
module Day8.Part1
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import Data.List
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import Data.Vect
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import Utils
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%default total
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--- TYPES
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Map : (h, w : Nat) -> Type
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Map h w = Grid h w (Maybe Char)
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--- PARSING
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parseInput : String -> Maybe (h ** w ** Map h w)
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parseInput inp = do
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(h ** w ** grid) <- parseGrid inp
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pure (h ** w ** map (map (filter (/='.') . Just)) grid)
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--- DATA
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frequencies : Map h w -> List Char
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frequencies mp = nub $ do
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row <- toList mp
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Just c <- toList row
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| Nothing => empty
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pure c
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antinodePos : {h, w : _} -> (a, b : Pos h w) -> Maybe (Pos h w)
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antinodePos (x, y) (x', y') =
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(,) <$> integerToFin (cast x * 2 - cast x') h
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<*> integerToFin (cast y * 2 - cast y') w
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antinodes : {h, w : _} -> Map h w -> Char -> List (Pos h w)
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antinodes mp c = do
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let poss = do
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i <- allFins h
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j <- allFins w
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guard (index (i, j) mp == Just c)
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pure (i, j)
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p1 <- poss
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p2 <- poss
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guard (p1 /= p2)
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toList (antinodePos p1 p2) <|> toList (antinodePos p2 p1)
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--- SOLUTION
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export
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solution : String -> Maybe Nat
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solution inp = do
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(h ** w ** mp) <- parseInput inp
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pure $ length $ nub $ frequencies mp >>= antinodes mp
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