java - Removing repeated characters in String

Question

I am having strings like this "aaaabbbccccaaddddcfggghhhh" and i want to remove repeated characters get a string like this "abcadcfgh".

A simplistic implementation for this would be :

for(Character c:str.toCharArray()){
  if(c!=prevChar){
    str2.append(c);
    prevChar=c;
  }

}

return str2.toString();

Is it possible to have a better implementation may be using regex?

Answer 1

You can do this:

"aaaabbbccccaaddddcfggghhhh".replaceAll("(.)\1+","$1");

The regex uses backreference and capturing groups.

The normal regex is (.)1+ but you've to escape the backslash by another backslash in java.

If you want number of repeated characters:

String test = "aaaabbbccccaaddddcfggghhhh";
System.out.println(test.length() - test.replaceAll("(.)\1+","$1").length());

Demo