d19

day19/d19p1.swift

@@ -0,0 +1,41 @@
+import Foundation
+
+enum Color: Character, CustomStringConvertible {
+    case r = "r"
+    case g = "g"
+    case u = "u"
+    case w = "w"
+    case b = "b"
+    var description: String { return String(self.rawValue) }
+}
+
+func readInput(_ filePath: String) throws -> ([[Color]], [[Color]]) {
+    let content = try String(contentsOfFile: filePath, encoding: .ascii)
+    let lines = content.split(separator: "\n")
+    let towels = lines[0].split(separator: ", ").map { $0.compactMap(Color.init) }
+    let patterns = lines[1..<lines.count].map { $0.compactMap(Color.init) }
+    return (towels, patterns)
+}
+
+var cache: [[Color]: Bool] = [:]
+func canMatch(_ pattern: [Color], _ towels: [[Color]]) -> Bool {
+    if pattern.count == 0 {
+        return true
+    }
+    if let cached = cache[pattern] {
+        return cached
+    }
+    for towel in towels {
+        if pattern.starts(with: towel) {
+            if canMatch(Array(pattern[towel.count..<pattern.count]), towels) {
+                cache[pattern] = true
+                return true
+            }
+        }
+    }
+    cache[pattern] = false
+    return false
+}
+
+let (towels, patterns) = try readInput(CommandLine.arguments[1])
+print(patterns.filter { canMatch($0, towels) }.count)