Adding to this, if you post a re-post you will be redirected to the old thread instead of your new one. So you will know that you're reposting!
(I was a little embarrassed when this happens to me at first, but I have gotten over it now. It's nice to have a computer fact check me. Even if it means my clever titles have to be thrown away!)
https://news.ycombinator.com/newsfaq.html