d06

day06/d06p1.swift

@@ -0,0 +1,80 @@
+import Foundation
+
+enum Direction {
+    case n, s, e, w
+    mutating func turnRight() {
+        switch self {
+        case .n:
+            self = .e
+        case .s:
+            self = .w
+        case .e:
+            self = .s
+        case .w:
+            self = .n
+        }
+    }
+    func move(x: Int, y: Int) -> (Int, Int) {
+        switch self {
+        case .n:
+            return (x-1, y)
+        case .s:
+            return (x+1, y)
+        case .e:
+            return (x, y+1)
+        case .w:
+            return (x, y-1)
+        }
+    }
+}
+
+struct Map {
+    var floor: [[Character]]
+    var guardX: Int
+    var guardY: Int
+    var guardDir = Direction.n
+    var done = false
+
+    func print() {
+        for (i, row) in floor.enumerated() {
+            Swift.print(String(row.enumerated().map {
+                ($0 == self.guardY && i == self.guardX) ? "G" : $1
+            }))
+        }
+    }
+
+    func countSteps() -> Int {
+        return floor
+            .map { $0.map { $0 == "^" ? 1 : 0 }.reduce(0, +) }
+            .reduce(0, +)
+    }
+
+    mutating func step() {
+        let (nextX, nextY) = guardDir.move(x: guardX, y: guardY)
+        if nextX < 0 || nextX >= floor.count
+           || nextY < 0 || nextY >= floor[0].count {
+            done = true
+        } else if floor[nextX][nextY] == "#" {
+            guardDir.turnRight()
+        } else {
+            floor[nextX][nextY] = "^"
+            (guardX, guardY) = (nextX, nextY)
+        }
+    }
+}
+
+func readInput(_ filePath: String) throws -> Map {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    let rows = content.split(separator: "\n").map(Array.init)
+    let (guardX, guardY) = rows.map {
+        $0.enumerated().compactMap { j, cell in cell == "^" ? j : nil }
+    }.enumerated().compactMap { $1.count > 0 ? ($0, $1[0]) : nil }[0]
+    return Map(floor: rows, guardX: guardX, guardY: guardY)
+}
+
+var map = try readInput(CommandLine.arguments[1])
+while !map.done {
+    map.step()
+}
+map.print()
+print(map.countSteps())