In contest Looksery Cup 2015, No one got accepted on 549E - Sasha Circle(You can see the standings). But the problem is only rated *2700. Maybe there is a mistake(although it is an old problem, or old problems have different rated standard)?

I noticed it was downvoted heavily. Why downvote it? May anyone tell me?

I always has difficulty in solving constructive problems.I usually think hard but I can't solve them.So how to solve them easily?Thanks a lot for your help.