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day6 part 1 only could not get part 2
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5 files changed

+244
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‎Sources/AdventOfCode.swift‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -7,6 +7,7 @@ let allChallenges: [any AdventDay] = [
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Day03(),
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Day04(),
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Day05(),
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Day06(),
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]
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@main

‎Sources/Day06.swift‎

Lines changed: 175 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,175 @@
1+
import Algorithms
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enum Direction: Int {
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case North = 0
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case East, South, West
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func heading() -> Coord {
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Coord.cross[rawValue]
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}
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static func fromHeading(coord: Coord) -> Self {
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Self(rawValue: Coord.cross.firstIndex { $0 == coord } ?? 0) ?? .North
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}
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func makeTurn() -> Self {
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Self(rawValue: self.rawValue + 1 % 4) ?? .North
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}
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}
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struct Guard {
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var pos: Coord
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var direction: Direction
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func nextPost() -> Coord {
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self.pos + self.direction.heading()
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}
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}
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struct Day06: AdventDay {
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var grid: Grid
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init(data: String) {
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grid = Grid(from: data)
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}
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func guardPatrol() -> (locations: Set<Coord>, steps: [Coord], obstacles: [Coord]) {
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var locations: Set<Coord> = Set()
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var steps: [Coord] = [Coord]()
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var obstacles: [Coord] = [Coord]()
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var officer = Guard(pos: grid.firstCoord(of: "^")!, direction: .North)
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while officer.pos.isInside(grid: grid) {
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// save position
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locations.insert(officer.pos)
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// move the guard
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let nextPos = officer.pos + officer.direction.heading()
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if !grid.includes(coord: nextPos) {
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obstacles.append(nextPos)
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steps.append(nextPos)
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break
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}
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if grid[nextPos] == "#" {
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obstacles.append(nextPos)
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// guard is blocked
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officer.direction = officer.direction.makeTurn()
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}
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// move officer one step
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officer.pos = officer.pos + officer.direction.heading()
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steps.append(officer.pos)
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}
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return (locations, steps, obstacles)
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}
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func doesComeBack(step: Coord) -> Bool {
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var officer = Guard(pos: grid.firstCoord(of: "^")!, direction: .North)
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var locations: [Coord] = [Coord]()
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while officer.pos.isInside(grid: grid) {
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locations.append(officer.pos)
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// move the guard
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let nextPos = officer.pos + officer.direction.heading()
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// behave like there is a real obstacle
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if nextPos == step {
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officer.direction = officer.direction.makeTurn()
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} else {
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if !grid.includes(coord: nextPos) {
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return false
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}
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if grid[nextPos] == "#" {
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// guard is blocked
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officer.direction = officer.direction.makeTurn()
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}
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}
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// check if we are going over our steps
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if locations.contains([officer.pos, nextPos]) {
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return true
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}
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// move officer one step
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officer.pos = officer.pos + officer.direction.heading()
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}
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return false
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}
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func part1() -> Int {
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guardPatrol().locations.count
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}
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// func part2() -> Int {
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// var potentialObstacles: [Coord] = [Coord]()
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// for step in Set(guardPatrol().steps) {
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// if doesComeBack(step: step) {
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// potentialObstacles.append(step)
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// }
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// }
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// return Set(potentialObstacles).count
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// }
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func isAValidLoop(wrappedOffset: Int, c: [Coord]) -> Coord? {
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if wrappedOffset == 0 {
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if c[c.startIndex].x > c[c.endIndex - 1].x {
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let coord = Coord(x: c[c.startIndex].x - 1, y: c[c.endIndex - 1].y)
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print("yes 0", coord)
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return coord
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}
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}
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if wrappedOffset == 1 {
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if c[c.startIndex].y > c[c.endIndex - 1].y {
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let coord = Coord(x: c[c.startIndex].x, y: c[c.startIndex].y - 1)
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print("yes 1", coord)
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return coord
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}
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}
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if wrappedOffset == 2 {
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if c[c.startIndex].x < c[c.endIndex - 1].x {
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let coord = Coord(x: c[c.endIndex - 1].x + 1, y: c[c.startIndex].y)
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print("yes 2", coord)
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return coord
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}
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}
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if wrappedOffset == 3 {
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if c[c.startIndex].y < c[c.endIndex - 1].y {
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let coord = Coord(x: c[c.endIndex - 1].x, y: c[c.startIndex].y + 1)
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print("yes 3", coord)
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return coord
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}
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}
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return nil
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}
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func part2() -> Int {
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var count = 0
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let obstacles = guardPatrol().obstacles
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var newObstacles: [Coord] = [Coord]()
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for (offset, candidates) in obstacles.windows(ofCount: 4).enumerated() {
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var c = Array(candidates)
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let wrappedOffset = offset % 4
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if let coord = isAValidLoop(wrappedOffset: wrappedOffset, c: c) {
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count += 1
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newObstacles.append(coord)
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}
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if offset > 4 {
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// TODO: this is not right
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for (idx, elem) in obstacles[0...0].enumerated() {
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print("trying", idx, elem)
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let wrappedOffset = offset % 4
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c[3] = elem
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if let coord = isAValidLoop(wrappedOffset: wrappedOffset, c: c) {
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count += 1
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newObstacles.append(coord)
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print(c)
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}
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}
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}
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}
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print(newObstacles)
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// 115 -> too low
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return count
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}
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}

‎Sources/Helpers/Coord.swift‎

Lines changed: 27 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -15,10 +15,14 @@ struct Coord {
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/// Offsets for the cross elements (+ shape)
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///
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static let cross = [
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//north
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Coord(x: 0, y: -1),
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// east
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Coord(x: 1, y: 0),
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// south
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Coord(x: 0, y: 1),
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// west
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Coord(x: -1, y: 0),
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Coord(x: 1, y: 0),
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]
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var cornerNeighbors: [Coord] {
@@ -41,6 +45,28 @@ struct Coord {
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4246
extension Coord: Equatable {}
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extension Coord: Hashable {}
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extension Coord: RawRepresentable {
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init?(rawValue: String) {
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let parts = rawValue.integers(separator: ",")
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x = parts[0]
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y = parts[1]
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}
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var rawValue: String {
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"(\(x),\(y))"
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}
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typealias RawValue = String
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}
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extension Coord: CustomStringConvertible {
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var description: String {
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"\(x),\(y)"
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}
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}
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4470
extension Coord: AdditiveArithmetic {
4571
static let zero = Coord(x: 0, y: 0)
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‎Sources/Helpers/Grid.swift‎

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -36,4 +36,14 @@ extension Grid {
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func includes(coord: Coord) -> Bool {
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coord.x >= 0 && coord.x <= self.width - 1 && coord.y >= 0 && coord.y <= self.height - 1
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}
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func firstCoord(of char: Character) -> Coord? {
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let index = self.raw.flatMap { $0 }.firstIndex(of: char)
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if let index = index {
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let x = index % self.width
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let y = index / self.width
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return Coord(x: x, y: y)
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}
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return nil
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}
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}

‎Tests/Day06.swift‎

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@@ -0,0 +1,31 @@
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import Testing
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@testable import aoc
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@Suite("Day06")
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struct Day06Tests {
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let testData = """
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....#.....
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.........#
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..........
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..#.......
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.......#..
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..........
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.#..^.....
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........#.
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#.........
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......#...
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"""
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@Test("part1")
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func testPart1() async throws {
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let challenge = Day06(data: testData)
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#expect(challenge.part1() == 41)
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}
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@Test("part2")
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func testPart2() async throws {
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let challenge = Day06(data: testData)
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#expect(challenge.part2() == 6)
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}
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}

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