2024-08

glguy · Dec 8, 2024 · 05931bc · 05931bc
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diff --git a/inputs/2024/08.txt b/inputs/2024/08.txt
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+...........g......................................
+......e.g......s.............R...........I........
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+.....g................U.............4.............
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+....a.....Q..........b........R..U...............1
+.S...T............s.............I.........f.......
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+.....Qa............A.G...K...........P............
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+...D...................................4.f........
+..................................................
+................k.......R....................t....
+.........T.e..............K........u.......t......
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+......S....a.............F...........KG...........
+....D...h......k..................................
+..D...............k............................4..
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diff --git a/solutions/solutions.cabal b/solutions/solutions.cabal
@@ -1147,3 +1147,8 @@ executable sln_2024_06
 executable sln_2024_07
   import:              day
   main-is:             2024/07.hs
+
+executable sln_2024_08
+  import:              day
+  main-is:             2024/08.hs
+  build-depends:       containers
diff --git a/solutions/src/2024/08.hs b/solutions/src/2024/08.hs
@@ -0,0 +1,49 @@
+{-# Language QuasiQuotes, ImportQualifiedPost #-}
+{-|
+Module      : Main
+Description : Day 8 solution
+Copyright   : (c) Eric Mertens, 2024
+License     : ISC
+Maintainer  : emertens@gmail.com
+
+<https://adventofcode.com/2024/day/8>
+
+-}
+module Main (main) where
+
+import Advent (getInputMap)
+import Advent.Coord (coordRow, coordCol, Coord (C))
+import Control.Monad (guard)
+import Data.List (nub, tails)
+import Data.Map qualified as Map
+
+-- | >>> :main
+-- 303
+-- 1045
+main :: IO ()
+main =
+ do input <- getInputMap 2024 8
+    let locs = Map.filter (\x -> length x > 1)
+             $ Map.fromListWith (++) [(v, [k]) | (k,v) <- Map.assocs input, v /= '.']
+    print $ length $ nub $
+     do posns <- Map.elems locs
+        x:ys <- tails posns
+        y <- ys
+        node <- [y + (y - x), x + (x - y)]
+        guard (Map.member node input)
+        pure node
+    print $ length $ nub $ concat (Map.elems locs) ++
+     do posns <- Map.elems locs
+        x:ys <- tails posns
+        y <- ys
+        z <- Map.keys input
+        guard (inlined x y z)
+        [z,x,y]
+
+inlined :: Coord -> Coord -> Coord -> Bool
+inlined x y z
+  | coordCol x == coordCol z = coordCol x == coordCol y
+  | otherwise = coordCol z /= coordCol y && slope z x == slope y x
+
+slope :: Coord -> Coord -> Rational
+slope (C y1 x1) (C y2 x2) = fromIntegral (y2-y1) / fromIntegral (x2-x1)