Removing repeated characters in String

Question

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

A simplistic implementati

Answer 1

You can do this:

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

Demo

Answer 2

With regex, you can replace (.)\1+ with the replacement string $1.

Answer 3

You can use Java's String.replaceAll() method to simply do this with a regular expression.

String s = "aaaabbbccccaaffffddcfggghhhh";
System.out.println(s.replaceAll("(.)\\1{1,}", "$1")) //=> "abcadcfgh"

Regular expression

(               group and capture to \1:
 .              any character except \n
)               end of \1
\1{1,}          what was matched by capture \1 (at least 1 times)

Answer 4

use this pattern /(.)(?=\1)/g and replace with nothing
Demo