d23p2

day23/d23p2.swift

@@ -0,0 +1,44 @@
+import Foundation
+
+typealias Network = [String: Set<String>]
+
+func readInput(_ filePath: String) throws -> Network {
+    var map: Network = [:]
+    try String(contentsOfFile: filePath, encoding: .ascii)
+        .split(separator: "\n").map { $0.split(separator: "-") }
+        .map { (String($0[0]), String($0[1])) }.forEach { m1, m2 in
+            map[m1, default: []].insert(m2)
+            map[m2, default: []].insert(m1)
+        }
+    return map
+}
+
+func bronkerbosch(
+    _ network: Network, r: Set<String>, p: Set<String>, x: Set<String>
+) -> Set<String>? {
+    if p.count == 0 && x.count == 0 {
+        return r
+    }
+    var maxClique: Set<String>? = nil
+    var nextP = p
+    var nextX = x
+    for v in p {
+        if let clique = bronkerbosch(network,
+            r: r.union([v]),
+            p: nextP.intersection(network[v]!),
+            x: nextX.intersection(network[v]!)
+        ) {
+            if clique.count > (maxClique ?? []).count {
+                maxClique = clique
+            }
+        }
+        nextP.remove(v)
+        nextX.insert(v)
+    }
+    return maxClique
+}
+            
+let conns = try readInput(CommandLine.arguments[1])
+let clique = bronkerbosch(conns, r: [], p: Set(conns.keys), x: [])
+print(Array(clique ?? []).sorted().joined(separator: ","))
+