Why some arc have discussions on codeforces but some don't?

I want to know that too

Long time no see, ARC.

It's ready to start,isn't it?

site is working?

Nice problems with small $$$N$$$ s.

Interesting and tricky problems!

Actually, C can be solved in $$$O(n)$$$.

Screencast with commentary

I solved A by counting inversions in $$$O(n$$$ $$$log$$$ $$$n)$$$. The idea is creating a new array $$$cnt$$$ where $$$cnt_i$$$ is the number of $$$j$$$ so that $$$i < j$$$ and $$$a_i > a_j$$$. Then the answer is the number of minimum elements in array $$$cnt$$$. However I can't quite explain why it worked.

For problem B I just try to move the number $$$n$$$ to position $$$n$$$, $$$n-1$$$ to position $$$n-1$$$. When you are down to $$$1$$$ and $$$2$$$, if $$$2$$$ is in front of $$$1$$$, the answer is $$$No$$$. The answer is $$$Yes$$$ otherwise.

Hello, I'm wondering what does the round-trip time mean. It seems that the outward time and the round-trip time are time points meaning start time and finish time but not a duration (which I am still not sure), but the given information says that the round-trip time is the sum of the outward and return times which really confuses me.

Actrually,I didn't understand problem A's statement even when I passed the problem.

I just guessed what it may wish me to do.

What is an ark everyone is talking about? I'm not sure what it is.