Hello!

Similar to last year, we are excited to invite you to **TOKI OSN Open Contest 2019** -- an online mirror contest for Indonesia national olympiad in informatics. This national olympiad is one of the stages required for our students to qualify to represent Indonesia in the International Olympiad in Informatics (IOI).

The contest is similar to IOI: 2 competition days (+ 1 trial session), each consisting of 3 IOI-style (partial, subtasked) problems to be solved in 5 hours. The schedule is as follows:

- Day 0: 1 July 2019 08:35 — 23:05 UTC (trial session)
- Day 1: 2 July 2019 02:35 — 23:05 UTC
- Day 2: 3 July 2019 02:35 — 23:05 UTC

Each contestant can select any 5-hour window within the time range to do the contest for each competition day. Each contestant may start the contest any time within the time range, by clicking a provided timer button.

All three contests are now available on TLX. Please register in those contests. You may need to register for a TLX account if you do not have one.

For more detailed information and rules, see our official website.

See you in the leaderboard! :)

**UPD1:** The contest is over, thanks for participating. We are still working on the post-contest blog summarizing the contest, including the problem repository and credits. Meanwhile, the scoreboard for TOKI OSN Open Contest 2019 is available here. The problems are also available for upsolving here (TLX account is required).

The first day contest will be available in less than an hour!

https://tlx.toki.id/contests/tooc-2019-day-1/

The second day contest will be available in less than an hour!

https://tlx.toki.id/contests/tooc-2019-day-2/

How can we submit for practice?

It's not been archived yet. It should be archived in this later https://training.ia-toki.org/archives/3.

The upsolving URL for OSN 2019 problems is available in the

UPD1of the post :) Thanks for participating!Is there any way to view the global results/ranking?

Yes! the result will be announced on osn2019.toki.id on July, 7th 2019 11:00 UTC. Sorry for the delay.

See you in the leaderboard! :)And we want to see that leaderboard :DWhen will we be able to see the leaderboard?

if you are one of contestant, you should be receiving an email. If not, you can see the scoreboard on July 7th, 11.00 UTC in this link https://osn2019.toki.id/

What is your score?

$$$571$$$ points. $$$71$$$ from $$$day1-C$$$, $$$100$$$ from other problems. I am so much regretting not trying some approaches for $$$day1-C$$$ $$$:($$$

What is your score?

I got 565 points(100-100-83-100-100-82). I used DP for day1C.

My solutionDp[i][j] is number of ways to get (i, j). If it is not 1 for some cell that belongs to path, you need to put 'x' in (i-1, j) or in (i, j-1) (which doesn't belong to jury's path) and update dps.

This solution got 9 points in last three test cases.

The leaderboard for TOKI OSN Open Contest 2019 is available in the

UPD1of the post :) Thanks for participating!Is there one full solution for the output only task from the first day of contest? I got 84 points by analyzing different cases.

You can nuke the problem by using min-cut.

Or actually, if you try to see which free cells can't be reached from start to end, surprisingly there are a lot (like ~90% even on the last testcase). So you can manually put optimal obstacles by hand.

The judge solution contains three different implementations, all find the optimal solution in under one second:

Given that each test case constraint (the fact that each test case is either C ≤ 16, empty grid, or single turn) is clearly mentioned in the problem statement, we don't see our solution as heuristics. And yes, we are aware of the O(N^3) maxflow solution and acknowledged this as a possible alternative solution.