diff -r 923b946347e6 -r e66bd5c563eb progs/catastrophic/catastrophic.rb
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/progs/catastrophic/catastrophic.rb	Mon Jul 27 11:02:48 2020 +0100
@@ -0,0 +1,35 @@
+# A case of catastrophic backtracking in Ruby
+#---------------------------------------------
+# example provided by Daniel Baldwin
+#
+# 
+# regex: (a?){n} a{n}
+# strings: aa...
+#
+# run on the command line with:
+#
+# $>  ruby catastrophic.rb
+#
+
+nums = (1..1000)
+
+#iterate through the nums 1-1000
+nums.each do |i|
+
+	start_time = Time.now
+	string = "a" * i
+
+        #create a new regular expression based on current value of i
+	re_str = "a?" * i + "+" + "a" * i
+	re = Regexp.new(re_str)
+
+        re.match(string)
+
+        #if re.match(string)
+	#	puts "matched string  a * #{i} with regex #{re}"
+	#else
+	#	puts "unmatched string a * #{i} with regex #{re}"
+	#end
+	
+  puts "#{i} %.5f" % (Time.now - start_time)
+end