If you post the same link as someone else shortly after them, you'll just get redirected the current discussion page and I believe it counts as an upvote to the

If you post the same link as someone else shortly after them, you'll just get redirected the current discussion page and I believe it counts as an upvote to the article. If sufficient time has elapsed since the last posting, HN allows links to be re-posted since peoples' viewpoints may have shifted, modern events may influence discussion, etc.