d11

day11/d11p2.swift

@@ -0,0 +1,39 @@
+import Foundation
+
+struct NumTimes : Hashable {
+    let num: Int
+    let times: Int
+}
+
+func readInput(_ filePath: String) throws -> [Int] {
+    return try String(contentsOfFile: filePath, encoding: .ascii)
+        .trimmingCharacters(in: .whitespacesAndNewlines)
+        .split(separator: " ").map { Int($0)! }
+}
+
+func evolve(_ num: Int) -> [Int] {
+    if num == 0 { return [1] }
+    let s = String(num)
+    if s.count.isMultiple(of: 2) {
+        return [
+            Int(String(Array(s)[s.count/2 ..< s.count]))!,
+            Int(String(Array(s)[0 ..< s.count/2]))!
+        ]
+    }
+    return [num * 2024]
+   
+}
+
+var cache: [NumTimes: Int] = [:]
+
+func count(_ num: Int, times: Int) -> Int {
+    if times == 0 { return 1 }
+    let key = NumTimes(num: num, times: times)
+    if let cached = cache[key] { return cached }
+    cache[key] = evolve(num).map { n in count(n, times: times-1) }.reduce(0, +)
+    return cache[key]!
+}
+
+let nums = try readInput(CommandLine.arguments[1])
+print(nums)
+print(nums.map { count($0, times: 75) }.reduce(0, +))