Pattern run-length encoding

Question

I'm trying to find the cleanest way to perform a run-length encoding based on patterns. The goal is to compress a string by factorizing a substring composed of several same patterns.

Original String:

start{3}{3}{3}{3}end

As you can see, there are 4 "{3}" patterns. It's possible to compress this String by expressing the run of 4 "{3}" patterns as $4{3}.

Compressed String I would like to obtain:

start$4{3}end

I tried the String.replaceAll(regex, replacement) method. I know that myString.replaceAll("\\{([^<])\\}", "$1") can replace a whole pattern by its value only but I can't find how to detect and count a same-pattern run length using regular expressions.

Is using regular expression a good idea or are there any other 'better' way to do this?

Answer 1

I just get the output as follows. There should be more efficient approach than this. But hopefully this will help you

    String s = "start{3}{3}{3}{3}end";
    String pString = "\\{3\\}";
    Pattern p = Pattern.compile(pString);
    Matcher m = p.matcher(s);

    int count = 0;
    while (m.find()) {
        count++;
    }
    System.out.println(s.replaceAll(pString, "-").replaceFirst("-{"+count+"}", "\\$"+count+pString));