Added 2022 day 13 solutions

HarshilShah · Dec 13, 2022 · b5b747b · b5b747b
1 parent b40fd7b
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Showing 2 changed files with 141 additions and 1 deletion.
diff --git a/2022/Sources/2022/Day13.swift b/2022/Sources/2022/Day13.swift
@@ -0,0 +1,140 @@
+import Algorithms
+import Collections
+import Foundation
+import RegexBuilder
+
+extension ComparisonResult {
+	static func comparing<C: Comparable>(_ a: C, b: C) -> ComparisonResult {
+		if a == b { return .orderedSame }
+		return a < b ? .orderedAscending : .orderedDescending
+	}
+}
+
+struct Packet: Hashable, CustomStringConvertible {
+	var items: [PacketItem]
+
+	func compared(with other: Packet) -> ComparisonResult {
+
+		for (i1, i2) in zip(items, other.items) {
+			let result = i1.compared(with: i2)
+			if result != .orderedSame {
+				return result
+			}
+		}
+
+		return .comparing(items.count, b: other.items.count)
+	}
+
+	static func parse(_ line: Substring) -> Packet {
+		var copy = line
+		return Packet(items: Packet.parse(&copy))
+	}
+
+	static func parse(_ line: inout Substring) -> [PacketItem] {
+		var current: Int?
+		var items: [PacketItem] = []
+
+		var offset = 0
+
+		while true {
+			defer { offset += 1 }
+
+			let char = line.dropFirst(offset).first!
+
+			if let wholeNumber = char.wholeNumberValue {
+				if current == nil {
+					current = 0
+				} else {
+					current! *= 10
+				}
+				current! += wholeNumber
+			} else {
+				if let c = current {
+					items.append(.integer(c))
+					current = nil
+				}
+
+				if char == "[" {
+					if offset == 0 { continue }
+					line = line.dropFirst(offset)
+					items.append(.packet(Packet(items: parse(&line))))
+					offset = 0
+				} else if char == "]" {
+					line = line.dropFirst(offset)
+					return items
+				}
+			}
+		}
+	}
+
+	var description: String {
+		return "[" +  items.map(\.description).joined(separator: ",") + "]"
+	}
+}
+
+enum PacketItem: Hashable, CustomStringConvertible {
+	case integer(Int)
+	case packet(Packet)
+
+	func compared(with other: PacketItem) -> ComparisonResult {
+		switch (self, other) {
+		case let (.integer(i1), .integer(i2)):
+			return .comparing(i1, b: i2)
+
+		case let (.packet(p1), .packet(p2)):
+			return p1.compared(with: p2)
+
+		case let (.integer(i), .packet(p)):
+			return Packet(items: [.integer(i)]).compared(with: p)
+
+		case let (.packet(p), .integer(i)):
+			return p.compared(with: Packet(items: [.integer(i)]))
+		}
+	}
+
+	var description: String {
+		switch self {
+		case .integer(let int): return int.description
+		case .packet(let packet): return packet.description
+		}
+	}
+}
+
+struct Day13: Day {
+	var input: String
+
+	init(input: String) {
+		self.input = input
+	}
+
+	func partOne() -> String {
+		input
+			.split(separator: "\n", omittingEmptySubsequences: true)
+			.map(Packet.parse)
+			.chunks(ofCount: 2)
+			.enumerated()
+			.filter { $0.element.first!.compared(with: $0.element.last!) != .orderedDescending }
+			.map { $0.offset + 1 }
+			.reduce(0, +)
+			.description
+	}
+
+	func partTwo() -> String {
+		let interlaced = [
+			Packet.parse("[[2]]"),
+			Packet.parse("[[6]]")
+		]
+
+		var all = input
+			.split(separator: "\n", omittingEmptySubsequences: true)
+			.map(Packet.parse)
+		all.append(contentsOf: interlaced)
+
+		all.sort(by: { $0.compared(with: $1) != .orderedDescending })
+
+		let i1 = all.firstIndex(of: interlaced[0])! + 1
+		let i2 = all.firstIndex(of: interlaced[1])! + 1
+
+		return (i1 * i2).description
+	}
+}
diff --git a/2022/Sources/2022/main.swift b/2022/Sources/2022/main.swift
@@ -1,6 +1,6 @@
 import Foundation
 
-typealias CurrentDay = Day12
+typealias CurrentDay = Day13
 
 let testInput = """
 <Insert your test input here>