What are the new improvements of OJ?

The new OJ saves all submissions so you don't have to worry about saving your code locally. The UI is redesigned from scratch to provide a much better user experience. There are many, many more improvements to come, stay tuned!

I have already signed up at leetcode.com, why can't I sign in to OJ?

You would need to create a new account at oj.leetcode.com. There is no plan to support account integration across these two sites.

I need to use the old OJ. Where can I find it?

You may continue to use the old OJ here. Please note that the old OJ will be retired and stop working on October 12, 12pm PST.

I had already solved quite a few problems in the old OJ. Could you please transfer my previously solved problems to the new OJ?

As the new OJ requires new registrations, there is no easy way to transfer your old submission data. You still have time to take note of the problems you solved before the old OJ is taken offline in October.