Java正则表达式的时间复杂度

Question

I wrote the following a java by using a regular expression to find a repeated String in the String s . Now I try to find the complexity of it, if any one know what is the complexity of it, please let me know.

           String s = "ABCABCAAAABBBBCCAAABCGABCABC";

           Pattern pattern = Pattern.compile("(?:([ABC])(?!\\1)([ABC])\\1\\2)+");
           Matcher matcher = pattern.matcher(s);

           while (matcher.find()) {
              System.out.print("FOUND");
           }

Answer 1

Regular expressions can/are implemented by finite state machines. So statemachine with some fixed number of states and a fixed maximum number (T) of transitions between these states.

For each character a transition is taken until it is rejected or accepted.

So you have O( String.length() * T) or O( String.length() ) as T is a constant.