Day 11

Author: peterkovacs

Sources/AdventOfCode.swift

@@ -78,7 +78,8 @@ extension ParsingCommand {
             Day7.self,
             Day8.self,
             Day9.self,
-            Day10.self
+            Day10.self,
+            Day11.self
         ]
     )
 

Sources/Day11.swift

@@ -0,0 +1,60 @@
+import ArgumentParser
+import Parsing
+import _math
+
+struct Day11: ParsingCommand {
+    @Argument var file: String = "11.txt"
+
+    static var parser: some Parser<Substring.UTF8View, [Int]> {
+        Many { Int.parser(of: Substring.UTF8View.self) }
+        separator: { Whitespace() }
+        terminator: {
+            Whitespace()
+            End()
+        }
+    }
+
+    func run() throws {
+        let input = try parsed(file: file).reduce(into: [Int:Int]()) { partialResult, i in
+            partialResult[i, default: 0] += 1
+        }
+
+        func iteration(partialResult: inout [Int: Int], i: (key: Int, value: Int)) {
+            if i.key == 0 { partialResult[1, default: 0] += i.value }
+            else if i.key.digits % 2 == 0 {
+                let (l, r) = i.key.split
+                partialResult[l, default: 0] += i.value
+                partialResult[r, default: 0] += i.value
+            } else {
+                partialResult[i.key * 2024, default: 0] += i.value
+            }
+        }
+
+        let part1 = (0..<25).reduce(into: input) { input, _ in
+            input = input.reduce(into: [Int:Int](), iteration)
+        }
+
+        print("Part 1", part1.map(\.value).reduce(0, +))
+
+
+        let part2 = (25..<75).reduce(into: part1) { input, i in
+            input = input.reduce(into: [Int:Int](), iteration)
+        }
+
+        print("Part 2", part2.map(\.value).reduce(0, +))
+    }
+}
+
+fileprivate extension Int {
+    var digits: Int {
+        return Int(log10(Double(self + 1)).rounded(.awayFromZero))
+    }
+
+    var split: (Int, Int) {
+        let digits = self.digits
+        let factor = Int(pow(10, Double(digits / 2)).rounded())
+        let left = self / factor
+        let right = self % factor
+        return (left, right)
+    }
+}