day8

Author: spaenleh

README.md

@@ -15,7 +15,7 @@ Below is my current advancement in Advent of code:
 | Day 5 | :star: (22min) | :star: (21min) |
 | Day 6 | :star: | :sad: |
 | Day 7 | :star: (45min) | :star: (33min) |
-| Day 8 |  |  |
+| Day 8 | :star: (20min) | :star: (16min) |
 | Day 9 |  |  |
 | Day 10 |  |  |
 | Day 11 |  |  |

Sources/AdventOfCode.swift

@@ -9,6 +9,7 @@ let allChallenges: [any AdventDay] = [
   Day05(),
   Day06(),
   Day07(),
+  Day08(),
 ]
 
 @main

Sources/Day08.swift

@@ -0,0 +1,66 @@
+import Algorithms
+
+struct Day08: AdventDay {
+  var antennaLocations: [Character: [Coord]] = [Character: [Coord]]()
+  var width: Int
+  var height: Int
+
+  init(data: String) {
+    let lines = data.lines()
+    height = lines.count
+    width = lines[0].count
+    for (colIdx, line) in lines.enumerated() {
+      for (rowIdx, char) in line.enumerated() {
+        if char != "." {
+          let currentPos = Coord(x: rowIdx, y: colIdx)
+          antennaLocations[char, default: [Coord]()].append(currentPos)
+        }
+      }
+    }
+  }
+
+  func isInside(_ node: Coord) -> Bool {
+    node.x >= 0 && node.x <= self.width - 1 && node.y >= 0 && node.y <= self.height - 1
+  }
+
+  func part1() -> Int {
+    var antiNodes: Set<Coord> = Set()
+    for (key, values) in antennaLocations {
+      for pair in values.combinations(ofCount: 2) {
+        let offset = pair[1] - pair[0]
+        [
+          pair[0] - offset,
+          pair[1] + offset,
+        ].filter { isInside($0) }.forEach {
+          antiNodes.insert($0)
+        }
+      }
+    }
+    return antiNodes.count
+  }
+
+  func walkAntiNodes(antenna: Coord, offset: Coord) -> [Coord] {
+    var allAntiNode = [Coord]()
+    var nodePos = antenna
+    repeat {
+      allAntiNode.append(nodePos)
+      nodePos += offset
+    } while isInside(nodePos)
+    return allAntiNode
+  }
+
+  func part2() -> Int {
+    var antiNodes: Set<Coord> = Set()
+    for (key, values) in antennaLocations {
+      for pair in values.combinations(ofCount: 2) {
+        let offset = pair[1] - pair[0]
+        var localNodes = walkAntiNodes(antenna: pair[0], offset: offset * -1)
+        localNodes.append(contentsOf: walkAntiNodes(antenna: pair[1], offset: offset))
+        localNodes.forEach {
+          antiNodes.insert($0)
+        }
+      }
+    }
+    return antiNodes.count
+  }
+}

Sources/Helpers/Coord.swift

@@ -80,6 +80,25 @@ extension Coord: AdditiveArithmetic {
   }
 }
 
+extension Coord: DurationProtocol {
+  static func / (lhs: Coord, rhs: Int) -> Coord {
+    return Self(x: lhs.x / rhs, y: lhs.y / rhs)
+  }
+
+  static func * (lhs: Coord, rhs: Int) -> Coord {
+    return Self(x: lhs.x * rhs, y: lhs.y * rhs)
+  }
+
+  static func / (lhs: Coord, rhs: Coord) -> Double {
+    return 0
+  }
+
+  static func < (lhs: Coord, rhs: Coord) -> Bool {
+    return false
+  }
+
+}
+
 extension Array where Array.Element == Coord {
   func included(in grid: Grid) -> Self {
     self.filter { $0.isInside(grid: grid) }

Tests/Day08.swift

@@ -0,0 +1,51 @@
+import Testing
+
+@testable import aoc
+
+@Suite("Day08")
+struct Day08Tests {
+  let testData = """
+    ............
+    ........0...
+    .....0......
+    .......0....
+    ....0.......
+    ......A.....
+    ............
+    ............
+    ........A...
+    .........A..
+    ............
+    ............
+    """
+
+  @Test("part1")
+  func testPart1() async throws {
+    let challenge = Day08(data: testData)
+    #expect(challenge.part1() == 14)
+  }
+
+  @Test("simple part 2")
+  func testSimplePart2() async throws {
+    let challenge = Day08(
+      data: """
+        T.........
+        ...T......
+        .T........
+        ..........
+        ..........
+        ..........
+        ..........
+        ..........
+        ..........
+        ..........
+        """)
+    #expect(challenge.part2() == 9)
+  }
+
+  @Test("part2")
+  func testPart2() async throws {
+    let challenge = Day08(data: testData)
+    #expect(challenge.part2() == 34)
+  }
+}