--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/catastrophic/catastrophic.swift	Tue Sep 29 19:35:11 2020 +0100
@@ -0,0 +1,43 @@
+// A case of catastrophic backtracking in Swift
+//---------------------------------------------
+// example provided by Martin Mikusovic
+//
+// regex: (a*)*b
+// strings: aa...a
+//
+// compile with
+//
+// swiftc catastrophic.swift
+//
+// run with for example
+//
+// time ./catastrophic 20
+
+import Foundation
+
+let args = CommandLine.arguments
+if args.count >= 2, let count = Int(args[1]) {
+    let s = String(repeating: "a", count: count)
+    calculateTime {
+        let _ = s ~= "(a*)*b"
+    }
+} else {
+    print("Please enter a valid number argument.")
+}
+
+func calculateTime(block: () -> ()) {
+    let start = DispatchTime.now()
+    block()
+    let end = DispatchTime.now()
+    let nanoTime = end.uptimeNanoseconds - start.uptimeNanoseconds
+    let timeInterval = Double(nanoTime) / 1_000_000_000
+    print("\(timeInterval) s")
+}
+
+extension String {
+    static func ~=(lhs: String, rhs: String) -> Bool {
+        guard let regex = try? NSRegularExpression(pattern: rhs) else { return false }
+        let range = NSRange(location: 0, length: lhs.utf16.count)
+        return regex.firstMatch(in: lhs, options: [], range: range) != nil
+    }
+}