AdventOfCode.com 2016 Day 1 Solution (http://adventofcode.com/2016/day/1) (Part 2)

Day1Part2.playground.swift

import Foundation

enum Axis {
    case X
    case Y
}

enum Instruction {
    case left (distance:Int)
    case right (distance:Int)
    
    init?(instructionString:String) {
        guard instructionString.characters.count >= 2 else { return nil }
        
        let firstIndex = instructionString.index(after: instructionString.startIndex)
        let direction = instructionString.substring(to: firstIndex).uppercased()
        let distance = instructionString.substring(from: firstIndex)
        
        guard let distanceInt = Int(distance), distanceInt > 0 else { return nil }
        
        switch direction {
        case "R":
            self = .right(distance: distanceInt)
        case "L":
            self = .left(distance: distanceInt)
        default:
            return nil
        }
    }
    
    var distance: Int {
        get {
            switch self {
            case let .left(dist): return dist
            case let .right(dist): return dist
            }
        }
    }
}

enum Direction {
    case North
    case South
    case East
    case West
    
    func turn(instruction:Instruction) -> Direction {
        if case .left(_) = instruction {
            switch self {
            case .North: return .West
            case .South: return .East
            case .East:  return .North
            case .West:  return .South
            }
        } else {
            switch self {
            case .North: return .East
            case .South: return .West
            case .East:  return .South
            case .West:  return .North
            }
        }
    }
    
    var axisMultiplier: (Axis, Int) {
        get {
            switch self {
            case .North: return (.X, 1)
            case .South: return (.X, -1)
            case .East:  return (.Y, 1)
            case .West:  return (.Y, -1)
            }
        }
    }
}

struct Location{
    let x: Int
    let y: Int
    let direction: Direction
    
}

// Implement Hashable so that Locations can be stored in a Set
extension Location: Hashable, Equatable {
    public var hashValue: Int {
        return x^y
    }
}

func ==(lhs: Location, rhs: Location) -> Bool {
    return lhs.x == rhs.x && lhs.y == rhs.y
}


// Day 1:
let inputString = "R5, L2, L1, R1, R3, R3, L3, R3, R4, L2, R4, L4, R4, R3, L2, L1, L1, R2, R4, R4, L4, R3, L2, R1, L4, R1, R3, L5, L4, L5, R3, L3, L1, L1, R4, R2, R2, L1, L4, R191, R5, L2, R46, R3, L1, R74, L2, R2, R187, R3, R4, R1, L4, L4, L2, R4, L5, R4, R3, L2, L1, R3, R3, R3, R1, R1, L4, R4, R1, R5, R2, R1, R3, L4, L2, L2, R1, L3, R1, R3, L5, L3, R5, R3, R4, L1, R3, R2, R1, R2, L4, L1, L1, R3, L3, R4, L2, L4, L5, L5, L4, R2, R5, L4, R4, L2, R3, L4, L3, L5, R5, L4, L2, R3, R5, R5, L1, L4, R3, L1, R2, L5, L1, R4, L1, R5, R1, L4, L4, L4, R4, R3, L5, R1, L3, R4, R3, L2, L1, R1, R2, R2, R2, L1, L1, L2, L5, L3, L1"

let inputs = inputString.components(separatedBy: ", ")

let instructions = inputs.flatMap { (insString) -> Instruction? in
    return Instruction(instructionString: insString)
}

// Just move one step in a certain direction
func performStep(direction:Direction, currentLocation:Location) -> Location {
    let axisMultiplier = direction.axisMultiplier
    let distanceOffset = axisMultiplier.1
    if axisMultiplier.0 == .Y {
        return Location(x: currentLocation.x, y: currentLocation.y + distanceOffset, direction: direction)
    } else {
        return Location(x: currentLocation.x + distanceOffset, y: currentLocation.y, direction: direction)
    }
}

var currentLocation = Location(x: 0, y: 0, direction: .North)
var visitedLocations:Set = [currentLocation] // Saves all of the unique locations that have been visisted

loopThroughInstructions: for instruction in instructions {
    let direction = currentLocation.direction.turn(instruction: instruction)
    for _ in 1...instruction.distance {
        currentLocation = performStep(direction: direction, currentLocation: currentLocation)
        if visitedLocations.contains(currentLocation) {
            break loopThroughInstructions  // We've found the current location in our list of visited places, so this is the answer
        } else {
            visitedLocations.insert(currentLocation)  // We haven't been here before, record that we have
        }
    }
}
let distance = abs(currentLocation.x) + abs(currentLocation.y)
print("Distance: \(distance)")