From b8fda3862dba1a24276e50b3899a95297a5a16af Mon Sep 17 00:00:00 2001
From: Sven Weidauer <sven@5sw.de>
Date: Sat, 17 Dec 2022 17:38:00 +0100
Subject: [PATCH] 2022 Day 16 Part 1

---
 2022/day16.swift | 73 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 2022/day16.swift

diff --git a/2022/day16.swift b/2022/day16.swift
new file mode 100644
index 0000000..9aaa2d4
--- /dev/null
+++ b/2022/day16.swift
@@ -0,0 +1,73 @@
+import Foundation
+import RegexBuilder
+
+struct Room {
+    var name: String
+    var flowRate: Int
+    var connections: [String]
+}
+
+
+let regex = #/Valve (?<room>[A-Z]{2}) has flow rate=(?<flow>\d+); tunnels? leads? to valves? (?<links>[A-Z]{2}(, [A-Z]{2})*)/#
+
+var rooms: [String: Room] = [:]
+
+for try await line in URL(fileURLWithPath: "day16.input").lines {
+    guard let match = try regex.wholeMatch(in: line) else {
+        fatalError("Invalid input: \(line)")
+    }
+    
+    rooms[String(match.room)] = Room(name: String(match.room), flowRate: Int(match.flow)!, connections: match.links.split(separator: ", ").map(String.init))
+}
+
+
+struct Path {
+    var rooms: [String] = []
+    var opened: Set<String> = []
+    var pressure: Int = 0
+}
+
+let totalTime = 30
+
+func findPath(from room: Room, previous: String? = nil, time: Int = totalTime, path: inout Path) {
+    guard time > 0 else { return }
+    
+    let best = findBest(path: path, room: room, previous: previous, turnedOn: false, time: time - 1)
+
+    if time >= 2, room.flowRate > 0 && path.opened.insert(room.name).inserted {
+        path.pressure += (time - 1) * room.flowRate
+        path = findBest(path: path, room: room, previous: previous, turnedOn: true, time: time - 2)
+    }
+
+    if best.pressure > path.pressure {
+        path = best
+    }
+}
+
+func findBest(path: Path, room: Room, previous: String? = nil, turnedOn: Bool, time: Int) -> Path {
+    var path = path
+    path.rooms.append("\(room.name)[\(room.flowRate)]\(turnedOn ? "*" : "")")
+    
+    var best = path
+    
+    for next in room.connections {
+        if !turnedOn && previous == next {
+            continue
+        }
+        
+        let nextRoom = rooms[next]!
+        
+        var nextPath = path
+        findPath(from: nextRoom, previous: room.name, time: time, path: &nextPath)
+        if nextPath.pressure > best.pressure {
+            best = nextPath
+        }
+    }
+    
+    return best
+}
+
+var path = Path()
+findPath(from: rooms["AA"]!, path: &path)
+print(path.rooms)
+print(path.pressure)
\ No newline at end of file