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2020/day12/main.swift

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+import Foundation
+let input = loadData(day: 12)
+
+let scanner = Scanner(string: input)
+
+var position = (north: 0, east: 0)
+var waypoint = (north: 1, east: 10)
+var direction = 0
+
+/*
+ while !scanner.isAtEnd {
+     guard let instruction = scanner.scanCharacter(), let value = scanner.scanInt() else {
+         fatalError("Invalid input")
+     }
+
+     switch instruction {
+     case "N": position.north += value
+     case "S": position.north -= value
+     case "E": position.east += value
+     case "W": position.east -= value
+     case "L": direction = (360 + direction - value) % 360
+     case "R": direction = (direction + value) % 360
+     case "F":
+         switch direction {
+         case 0: position.east += value
+         case 90: position.north -= value
+         case 180: position.east -= value
+         case 270: position.north += value
+         default: fatalError("Invalid direction")
+         }
+     default: fatalError("Invalid command")
+     }
+ }
+ */
+
+func turn(_ degrees: Int) -> (north: Int, east: Int) {
+    switch degrees {
+    case 0: return waypoint
+    case 90: return (-waypoint.east, waypoint.north)
+    case 180: return (-waypoint.north, -waypoint.east)
+    case 270: return (waypoint.east, -waypoint.north)
+    default: fatalError("Invalid direction")
+    }
+}
+
+while !scanner.isAtEnd {
+    guard let instruction = scanner.scanCharacter(), let value = scanner.scanInt() else {
+        fatalError("Invalid input")
+    }
+
+    switch instruction {
+    case "N": waypoint.north += value
+    case "S": waypoint.north -= value
+    case "E": waypoint.east += value
+    case "W": waypoint.east -= value
+    case "R": waypoint = turn(value)
+    case "L": waypoint = turn(360 - value)
+    case "F":
+        position.north += value * waypoint.north
+        position.east += value * waypoint.east
+    default: fatalError("Invalid command")
+    }
+}
+
+print(abs(position.north) + abs(position.east))