Add 2016 solutions

2016/AoC2016.playground/Pages/Day 1.xcplaygroundpage/Contents.swift

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+import Foundation
+
+let input = """
+L5, R1, R4, L5, L4, R3, R1, L1, R4, R5, L1, L3, R4, L2, L4, R2, L4, L1, R3, R1, R1, L1, R1, L5, R5, R2, L5, R2, R1, L2, L4, L4, R191, R2, R5, R1, L1, L2, R5, L2, L3, R4, L1, L1, R1, R50, L1, R1, R76, R5, R4, R2, L5, L3, L5, R2, R1, L1, R2, L3, R4, R2, L1, L1, R4, L1, L1, R185, R1, L5, L4, L5, L3, R2, R3, R1, L5, R1, L3, L2, L2, R5, L1, L1, L3, R1, R4, L2, L1, L1, L3, L4, R5, L2, R3, R5, R1, L4, R5, L3, R3, R3, R1, R1, R5, R2, L2, R5, L5, L4, R4, R3, R5, R1, L3, R1, L2, L2, R3, R4, L1, R4, L1, R4, R3, L1, L4, L1, L5, L2, R2, L1, R1, L5, L3, R4, L1, R5, L5, L5, L1, L3, R1, R5, L2, L4, L5, L1, L1, L2, R5, R5, L4, R3, L2, L1, L3, L4, L5, L5, L2, R4, R3, L5, R4, R2, R1, L5
+"""
+
+enum Direction {
+    case north
+    case east
+    case south
+    case west
+
+    func turnLeft() -> Direction {
+        switch self {
+        case .north: return .west
+        case .east: return .north
+        case .south: return .east
+        case .west: return .south
+        }
+    }
+
+    func turnRight() -> Direction {
+        switch self {
+        case .north: return .east
+        case .east: return .south
+        case .south: return .west
+        case .west: return .north
+        }
+    }
+
+    func move(units: Int) -> (north: Int, east: Int) {
+        switch self {
+        case .north: return (units, 0)
+        case .east: return (0, units)
+        case .south: return (-units, 0)
+        case .west: return (0, -units)
+        }
+    }
+}
+
+struct Position: Hashable {
+    var heading: Direction = .north
+    var north: Int = 0
+    var east: Int = 0
+
+    mutating func move(left: Bool, units: Int) -> [Position] {
+        heading = left ? heading.turnLeft() : heading.turnRight()
+        let (north, east) = heading.move(units: 1)
+
+        var result: [Position] = []
+        for _ in 0..<units {
+            self.north += north
+            self.east += east
+            result.append(self)
+        }
+
+        return result
+    }
+
+    static func == (lhs: Position, rhs: Position) -> Bool {
+        lhs.north == rhs.north && lhs.east == rhs.east
+    }
+
+    func hash(into hasher: inout Hasher) {
+        hasher.combine(north)
+        hasher.combine(east)
+    }
+
+    var distance: Int {
+        abs(north) + abs(east)
+    }
+}
+
+let scanner = Scanner(string: input)
+
+extension Scanner {
+    func scanDirection() -> Bool {
+        if scanString("L") != nil { return true }
+        if scanString("R") != nil { return false }
+        fatalError("Invalid direction")
+    }
+
+    func scanMove() -> (Bool, Int) {
+        let direction = scanDirection()
+        guard let units = scanInt() else {
+            fatalError("Invalid distance")
+        }
+
+        guard isAtEnd || scanString(",") != nil else {
+            fatalError("Missing ,")
+        }
+
+        return (direction, units)
+    }
+}
+
+var position = Position()
+var visited: Set<Position> = [position]
+var foundPart2 = false
+while !scanner.isAtEnd {
+    let (direction, units) = scanner.scanMove()
+    let path = position.move(left: direction, units: units)
+
+    for position in path {
+        if !foundPart2 && !visited.insert(position).inserted {
+            print("Part 2: Visited again: \(position.distance): \(position.north)n, \(position.east)e")
+            foundPart2 = true
+            break
+        }
+    }
+}
+
+print("Part 1:", position.distance)