d13

day13/d13p2.swift

@@ -0,0 +1,50 @@
+import Foundation
+
+struct Machine {
+    let (aX, aY): (Int, Int)
+    let (bX, bY): (Int, Int)
+    let (przX, przY): (Int, Int)
+    func solve() -> Int? {
+        let d = aX*bY - aY*bX
+        let (a, ar) = (przX*bY - przY*bX).quotientAndRemainder(dividingBy: d)
+        let (b, br) = (przY*aX - przX*aY).quotientAndRemainder(dividingBy: d)
+        if ar == 0 && br == 0 {
+            return a*3 + b
+        }
+        return nil
+    }
+}
+
+func readInput(_ filePath: String) throws -> [Machine] {
+    let btnA = try Regex(#"Button A: X\+([0-9]+), Y\+([0-9]+)"#)
+    let btnB = try Regex(#"Button B: X\+([0-9]+), Y\+([0-9]+)"#)
+    let prize = try Regex(#"Prize: X=([0-9]+), Y=([0-9]+)"#)
+
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    var machines: [Machine] = []
+    var (aX, aY, bX, bY): (Int, Int, Int, Int) = (-1, -1, -1, -1)
+    content.split(separator: "\n").forEach { line in
+        if let m = line.wholeMatch(of: btnA) {
+            aX = Int(m.output[1].substring!)!
+            aY = Int(m.output[2].substring!)!
+        } else if let m = line.wholeMatch(of: btnB) {
+            bX = Int(m.output[1].substring!)!
+            bY = Int(m.output[2].substring!)!
+        } else if let m = line.wholeMatch(of: prize) {
+            machines.append(Machine(aX: aX, aY: aY, bX: bX, bY: bY,
+                przX: 10000000000000 + Int(m.output[1].substring!)!,
+                przY: 10000000000000 + Int(m.output[2].substring!)!
+            ))
+        }
+    }
+    return machines
+}
+
+let machines = try readInput(CommandLine.arguments[1])
+var answer = 0
+machines.forEach { m in
+    print(m)
+    if let cost = m.solve() { answer += cost }
+}
+print(answer)
+