eldridge.cam
Advent of Code solutions
2025 day 4
+26
2025/4/p1.hs
+26
2025/4/p1.hs
···
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import Data.List ((!?))
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import Text.Parsec
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surrounding x y =
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[ (x - 1, y - 1),
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(x, y - 1),
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(x + 1, y - 1),
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(x - 1, y),
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(x + 1, y),
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(x - 1, y + 1),
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(x, y + 1),
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(x + 1, y + 1)
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]
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answer input =
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length
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[ 1 | y <- [0 .. length grid - 1],
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x <- [0 .. (length $ grid !! y) - 1],
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grid !! y !! x == '@',
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length [1 | (x2, y2) <- surrounding x y,
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((grid !? y2) >>= (!? x2)) == (Just '@')] < 4
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]
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where
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Right grid = parse ((many $ oneOf "@.") `sepEndBy` char '\n') "" input
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main = getContents >>= print . answer
+27
2025/4/p1.tri
+27
2025/4/p1.tri
···
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import "trilogy:debug" use dbg, tap
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import "trilogy:core" use length
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import "trilogy:io" use readall
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import "trilogy:grid" as grid
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import "trilogy:number" use im, re, swap
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import "trilogy:array" use map, filter
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import "trilogy:parsec" use parse, end_by, char, many, char_of
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func get g p = with g.(swap <| im p).(re p) when 'mia cancel '.' else yield
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proc main!() {
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let rows = parse (end_by (char '\n') <| many <| char_of "@.") readall!()
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let g = grid::from!(rows)
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let mut count = 0
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for pos:'@' in g {
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let around = grid::surrounding pos
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# TODO: something is wrong when passing the large record around, the runtime freezes
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# up. Accessing from the array here instead works a little better, but it's still way
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# too slow, and not linearly
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|> map (get rows)
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|> filter ((==) '@')
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|> length
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if around < 4 { count += 1 }
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}
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dbg!(count)
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}
+31
2025/4/p2.hs
+31
2025/4/p2.hs
···
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import Data.List ((!?))
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import Text.Parsec
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surrounding x y =
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[ (x - 1, y - 1),
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(x, y - 1),
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(x + 1, y - 1),
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(x - 1, y),
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(x + 1, y),
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(x - 1, y + 1),
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(x, y + 1),
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(x + 1, y + 1)
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]
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at grid x y = case ((grid !? y) >>= (!? x)) of
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Just ch -> ch
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Nothing -> '.'
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isBlocked grid (x, y) = at grid x y == '@'
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clean grid = if cleaned == grid then grid else clean cleaned
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where
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cleaned = [[if at grid x y == '.' || (length $ filter (isBlocked grid) $ surrounding x y) < 4 then '.' else '@' | x <- [0 .. (length $ grid !! y) - 1]] | y <- [0 .. length grid - 1]]
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answer input = init - final
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where
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Right grid = parse ((many $ oneOf "@.") `sepEndBy` char '\n') "" input
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init = length $ filter ((==) '@') input
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final = length $ filter ((==) '@') $ concat $ (clean grid)
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main = getContents >>= print . answer