From 7ce30d3ab60f066c05d0f387fc213ef43083d741 Mon Sep 17 00:00:00 2001
From: Jordan Doyle <jordan@doyle.la>
Date: Wed, 6 Dec 2023 16:18:49 +0000
Subject: [PATCH] Add day 3

---
 3.hs | 87 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100755 3.hs

diff --git a/3.hs b/3.hs
new file mode 100755
index 0000000..b3a1d06
--- /dev/null
+++ b/3.hs
@@ -0,0 +1,87 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i runghc -p "haskellPackages.ghcWithPackages (pkgs: with pkgs; [ ])"
+import Data.Char (isNumber)
+import Data.List (findIndices)
+
+{- https://adventofcode.com/2023/day/3 -}
+
+main = do
+  input <- getContents
+  let (schematics, symbols) = takeSymbols input
+  print $ sum $ part1FindNumbersAdjacentToSchematic schematics symbols
+  print $ sum $ map product $ part2FindGearPartNumbers schematics symbols
+
+-- find all the part numbers (schematics that are adjacent to a symbol)
+part1FindNumbersAdjacentToSchematic :: [Schematic] -> [Symbol] -> [Int]
+part1FindNumbersAdjacentToSchematic schematics symbols = map partNumber $ filter (isSchematicAdjacentToAnySymbol symbols) schematics
+
+-- find all part numbers for gears (schematics that are adjacent to exactly two symbols)
+part2FindGearPartNumbers :: [Schematic] -> [Symbol] -> [[Int]]
+part2FindGearPartNumbers schematics symbols = map (map partNumber) $ filter (\inner -> length inner == 2) $ map (findSchematicsAdjacentToSymbol schematics) symbols
+
+-- returns all schematics that are adjacent to the given symbol
+findSchematicsAdjacentToSymbol :: [Schematic] -> Symbol -> [Schematic]
+findSchematicsAdjacentToSymbol schematics symbol = filter (`isSchematicAdjacent` symbol) schematics
+
+-- returns true, if the given schematic is adjacent to any of the given symbols
+isSchematicAdjacentToAnySymbol :: [Symbol] -> Schematic -> Bool
+isSchematicAdjacentToAnySymbol symbol schematic = any (isSchematicAdjacent schematic) symbol
+
+-- returns true, if the given schematic is directly adjacent to the given symbol
+isSchematicAdjacent :: Schematic -> Symbol -> Bool
+isSchematicAdjacent sc sy = isAdjacent (symbolCoords sy) (schematicCoords sc)
+
+-- returns true, grid position (px, py) is adjacent to single height multi column grid position (rx, ry, width)
+isAdjacent :: (Int, Int) -> (Int, Int, Int) -> Bool
+isAdjacent (px, py) (rx, ry, width) =
+  let leftX = rx
+      rightX = rx + width - 1
+      upperY = ry + 1
+      lowerY = ry - 1
+   in (px >= leftX - 1 && px <= rightX + 1 && py == ry) -- adjacent horizontally
+        || (py == upperY || py == lowerY) && (px >= leftX && px <= rightX) -- adjacent vertically
+        || (px == leftX - 1 || px == rightX + 1) && (py == upperY || py == lowerY) -- adjacent diagonally
+
+data Schematic = Schematic
+  { partNumber :: Int,
+    schematicCoords :: (Int, Int, Int)
+  }
+  deriving (Show)
+
+data Symbol = Symbol
+  { symbolCoords :: (Int, Int),
+    symbolType :: Char
+  }
+  deriving (Show)
+
+-- parse the entire input
+takeSymbols :: String -> ([Schematic], [Symbol])
+takeSymbols input = takeSymbol input Nothing (0, 0) [] []
+
+-- recursively parses the input character by character
+takeSymbol :: String -> Maybe Schematic -> (Int, Int) -> [Schematic] -> [Symbol] -> ([Schematic], [Symbol])
+takeSymbol "" Nothing _ schematicAcc symbolAcc = (schematicAcc, symbolAcc)
+takeSymbol "" (Just inProgressSchematic) _ schematicAcc symbolAcc = (schematicAcc ++ [inProgressSchematic], symbolAcc)
+takeSymbol (x : xs) inProgressSchematic (posX, posY) schematicAcc symbolAcc =
+  case x of
+    _ | isNumber x -> takeSymbol xs (Just $ appendToSchematic inProgressSchematic (posX, posY) (read [x])) (posX + 1, posY) schematicAcc symbolAcc
+    '.' -> takeSymbol xs Nothing (posX + 1, posY) (maybeAppend schematicAcc inProgressSchematic) symbolAcc
+    '\n' -> takeSymbol xs Nothing (0, posY + 1) (maybeAppend schematicAcc inProgressSchematic) symbolAcc
+    _ -> takeSymbol xs Nothing (posX + 1, posY) (maybeAppend schematicAcc inProgressSchematic) (symbolAcc ++ [buildSymbol posX posY x])
+
+-- appends a character to the schematic, creating a new schematic if one isn't already instantiated
+appendToSchematic :: Maybe Schematic -> (Int, Int) -> Int -> Schematic
+appendToSchematic (Just schematic) _ c =
+  let (x, y, n) = schematicCoords schematic
+      currPartNumber = partNumber schematic
+   in schematic {partNumber = currPartNumber * 10 + c, schematicCoords = (x, y, n + 1)}
+appendToSchematic Nothing (x, y) c = Schematic {partNumber = c, schematicCoords = (x, y, 1)}
+
+-- append a Maybe Schematic to [Schematic]
+maybeAppend :: [Schematic] -> Maybe Schematic -> [Schematic]
+maybeAppend out (Just new) = out ++ [new]
+maybeAppend out Nothing = out
+
+-- easy constructor for a Symbol
+buildSymbol :: Int -> Int -> Char -> Symbol
+buildSymbol x y symbolType = Symbol {symbolCoords = (x, y), symbolType}
--
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