We will hold Dwango Programming Contest 6th.

- Contest URL: https://atcoder.jp/contests/dwacon6th-prelims
- Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20200111T2000&p1=248 (an hour earlier than usual time)
- Duration: 120 minutes
- Number of Tasks: 5
- Writer: dwango competitive programming club
- Rated range: ~ 2799

The point values will be announced later.

We are looking forward to your participation!

Hope this contest isnt unrated too.

How do you solve task B? I didn't even understand the statement.

Editorial of A, B are available.

can you explain the editorial of B ?

How to solve D?

I was adding numbers one by one from postion $$$1$$$ to position $$$n$$$. Let's say we are adding currently element at position $$$i$$$ (there is $$$n-i+1$$$ possible values). In case some element can not be right for all other elements (rest $$$n-i$$$ elements have same $$$a_i$$$ value), then put that element on position $$$i$$$. Otherwise put smallest or second smallest element on position $$$i$$$.

Obviously we can not get smaller lex permutation than this one, but also it is possible that last two elements are bad in the permutation:

For example case:

$$$ n = 5$$$

$$$a = [2, 3, 1, 5, 4]$$$

My algorithm will give result: $$$[1, 3, 2, 4, 5]$$$ and it is incorrect result. But we can make it better, just pick last three elements and try every permutation — at least one of permatutions will be valid (that is reason because there is no answer just for $$$n = 2$$$).

I would had much apreciated to get a "warning" or something before haveing submitted A. Because then I would had read the other problems beforehand, and propably would not have participated at all.

How to solve C?

There is an editorial available. editorial

Edit: Just saw that the english version is not available for all problems, sorry.

Here's a nice analogy: you can interpret the problem as follows- There's a $$$k\times n$$$ grid. First you have to distribute $$$a_i$$$ black hokey pucks among the $$$n$$$ cells of the $$$i$$$-th row (for each $$$i$$$). Then you have to distribute $$$n$$$ red hockey pucks on top of the $$$\sum a_i$$$ black pucks such that every column has exactly one red puck. Count how many ways are there to do that.

How to solve B , i did not understood the editorial

Did it say that the English version of the Editorial would come out today?

I still don't know how to solve C

If you get it from somewhere or translate and understand using the Google-Translate Api then please share it here.

Hi, it's been more than a day and the editorials are not out, as promised. It would be great if you could upload them since the questions were interesting :)

editorial is out already .... on yesterday

The English one for the later problems isn't.

In problem B editorial how to prove the probabilities stated are correct. For example it is given In order for Slime i − 2 to cover the section from xi to xi+1, both Slime i − 1 and i need to be chosen earlier than Slime i − 2, so pi,i = 1/3. How to prove it ?

Where can we see the data? I found that it isn't in the dropbox...

can someone please explain the solution for problem C? I am not able to understand tutorial for the problem