notepad++ - Regex to remove duplicate letters

Question

I have a document in Notepad++ where each line can have any combination of characters. For example:

RRGG
U
XB
UUGG
UG

What I would like, is a regex to remove any duplicate characters. So, given the above, I would be left with:

RG
U
XB
UG
UG

I've tried finding ([a-z]) and replacing with 1 based on something I'd seen online, but I got nothing. I've even tried finding ([a-z])+, but that just got me the last letter on the line(not sure why I thought that would work, other than I'm horrible at regex). I also don't want to get rid of any whitespace, or empty lines. What's the best way to do this?

Answer 1

Find:

([A-Z])1+

Replace with:

1