d14

day14/d14p1.swift

@@ -0,0 +1,51 @@
+import Foundation
+
+let (w, h) = (101, 103)
+
+infix operator %%: MultiplicationPrecedence
+func %%<T: BinaryInteger>(lhs: T, rhs: T) -> T {
+    return (lhs % rhs + rhs) % rhs
+}
+
+struct Robot : CustomStringConvertible {
+    var (x, y): (Int, Int)
+    let (vx, vy): (Int, Int)
+    var description: String { return "p=(\(x), \(y)) v=(\(vx), \(vy))" }
+
+    mutating func move() {
+        x = (x + vx) %% w
+        y = (y + vy) %% h
+    }
+}
+
+func readInput(_ filePath: String) throws -> [Robot] {
+    let robot = try Regex(#"p=([0-9]+),([0-9]+) v=([0-9-]+),([0-9-]+)"#)
+    var robots: [Robot] = []
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    content.split(separator: "\n").forEach { line in
+        if let m = line.wholeMatch(of: robot) {
+            robots.append(Robot(
+                x: Int(m.output[1].substring!)!,
+                y: Int(m.output[2].substring!)!,
+                vx: Int(m.output[3].substring!)!,
+                vy: Int(m.output[4].substring!)!
+            ))
+        }
+    }
+    return robots
+}
+
+var robots = try readInput(CommandLine.arguments[1])
+for _ in 0..<100 {
+    for i in 0..<robots.count {
+        robots[i].move()
+    }
+}
+var (ul, ur, ll, lr) = (0, 0, 0, 0)
+for robot in robots {
+    if robot.x < w/2 && robot.y < h/2 { ul += 1 }
+    if robot.x > w/2 && robot.y < h/2 { ur += 1 }
+    if robot.x < w/2 && robot.y > h/2 { ll += 1 }
+    if robot.x > w/2 && robot.y > h/2 { lr += 1 }
+}
+print("\(ul) x \(ur) x \(ll) x \(lr) = \(ul * ur * ll * lr)")