The onsite events of CODE FESTIVAL 2016 will start soon. I'll keep posting commentaries here. All times written here are Japanese Standard Time, which is UTC+9 or Moscow Time + 6.

[25th, Friday 21:25]

As the name of the contest may suggest, there are lots of events, including five contests:

• CODE FESTIVAL 2016 Final

• CODE FESTIVAL 2016 Exhibition

• CODE FESTIVAL 2016 Elimination Tournament (3 rounds)

• CODE FESTIVAL 2016 Relay

• CODE FESTIVAL 2016 Grand Final

Some events are even overlapping so you have to choose one of them.

For those who can't attend the onsite events, there will be open contests. Please check the details at https://atcoder.jp/post/58 (here times are also written in JST). The Finals will start at Saturday 12:30, UTC+9.

[26th, Saturday 16:19]

Final Standings: https://cf16-final.contest.atcoder.jp/standings

The winner of Final is tourist. Congratulations!

The winner of Grand Final is W4yneb0t. Congratulations!

Semifinal 1 will start in 43 minutes.

Broadcast: https://www.twitch.tv/topcoder_official

TCO Blog (I'm the blog writer): http://tco16.topcoder.com/blog/

AtCoder Grand Contest 007 will be held on Saturday (time). The writer is dreamoon_love_AA.

Contest Link

Contest Announcement

The point values are 200 — 400 — 1000 — 1200 (600) — 1400 — 1500.

Let's discuss problems after the contest.

AtCoder Grand Contest 006 will be held on Saturday (time). The writer is sugim48.

Note that this time the contest duration is 130 minutes (20 minutes longer than usual).

Contest Link

Contest Announcement

The point values are 200 — 400 — 800 — 1300 — 1500 — 1700.

Let's discuss problems after the contest.

CODE FESTIVAL 2016 Qualification Round C will be held on Sunday Monday (time). The writer is sigma425.

Contest Link

Contest Announcement

This is one of the three qualification rounds of CODE FESTIVAL. Top 5 foreign students of this round will qualify. If you are eligible for the onsite contest, please don't forget to fill the form at https://krs.bz/rhd-itm/m/code_fes_2016. Please check the detail of the tournament at http://codeforces.net/blog/entry/46647.

The contest duration is 2 hours, and there will be 5 problems. The first 4 problems are mainly used for choosing domestic students and much easier than other tournament competitions. However, we added one more problem and we hope this is interesting enough for choosing top 5 qualifiers. (Anyway, most probably the qualifiers will be determined by the speed of solving all problems). Note that there is no time penalty for incorrect submissions. The time penalty is MAX, not SUM.

The point values are 100 — 200 — 400 — 800 — 1200. If you are unfamiliar with AtCoder System, 2X-point problem in AtCoder is as hard as TopCoder's d1 X-point problem.

Let's discuss problems after the contest.

UPD: Fixed the date.

UPD: The top 5 were jcvb, W4yneb0t, riadwaw, xyz111, and xyz2606. Congratulations!

UPD: Since wwwwodddd turned out to be a cheater, this account was excluded from the contest and banned from AtCoder. The qualifiers and the ratings were recomputed.

CODE FESTIVAL 2016 Qualification Round B will be held on Monday (time). The writer is DEGwer.

Contest Link

Contest Announcement

This is one of the three qualification rounds of CODE FESTIVAL. Top 5 foreign students of this round will qualify. If you are eligible for the onsite contest, please don't forget to fill the form at https://krs.bz/rhd-itm/m/code_fes_2016. Please check the detail of the tournament at http://codeforces.net/blog/entry/46647.

The contest duration is 2 hours, and there will be 5 problems. The first 4 problems are mainly used for choosing domestic students and much easier than other tournament competitions. However, we added one more problem and we hope this is interesting enough for choosing top 5 qualifiers. (Anyway, most probably the qualifiers will be determined by the speed of solving all problems). Note that there is no time penalty for incorrect submissions. The time penalty is MAX, not SUM.

The point values are 100 — 200 — 500 — 700 — 1100. If you are unfamiliar with AtCoder System, 2X-point problem in AtCoder is as hard as TopCoder's d1 X-point problem.

Let's discuss problems after the contest.

UPD: Among the top 5 foreign participants, Arterm has already qualified from round A, and matthew99, Reyna, SkyDec are too young. Congratulations to Merkurev, polequoll, fqw, sevenkplus, and Zlobober! Note that this information is unofficial, and it is possible that some of them don't want to participate in finals (or ineligible).

Let's discuss problems.

How to solve 8? I have no idea at all and finally decided to believe that we don't need nested addition/subtraction blocks, but it got WA. It seems there are harder cases.

How to solve 12? Essentially it reduces to the following: you are given a circle C and a point P. Find the movement of a point on C whose angular velocity is proportional to the distance from P. Is numerical integration accurate enough?

AtCoder Grand Contest 005 will be held on Saturday (time). The writer is yosupo.

Contest Link

Contest Announcement

Let's discuss problems after the contest.

CODE FESTIVAL 2016 Qualification Round A will be held on Saturday (time). The writer is sugim48.

Contest Link

Contest Announcement

This is one of the three qualification rounds of CODE FESTIVAL. Top 10 foreign students of this round will qualify. If you are eligible for the onsite contest, please don't forget to fill the form at https://krs.bz/rhd-itm/m/code_fes_2016. Please check the detail of the tournament at http://codeforces.net/blog/entry/46647.

The contest duration is 2 hours, and there will be 5 problems. The first 4 problems are mainly used for choosing domestic students and much easier than other tournament competitions. However, we added one more problem and we hope this is interesting enough for choosing top 10 qualifiers. (Anyway, most probably the qualifiers will be determined by the speed of solving all problems). Note that there is no time penalty for incorrect submissions. The time penalty is MAX, not SUM.

The point values are 100 — 200 — 400 — 800 — 1200. If you are unfamiliar with AtCoder System, 2X-point problem in AtCoder is as hard as TopCoder's d1 X-point problem.

Let's discuss problems after the contest.

UPD: Congratulations to tourist, Endagorion, LHiC, Arterm, Kostroma, mmaxio, Um_nik, ainu7, malcolm, FatalEagle! (I don't know who is eligible and this is not the official information, please let me know if some of them won't come.)

Note: The contest was moved to Sunday in order to avoid collision with TCO Russia.

AtCoder Grand Contest 004 will be held on Sunday (time). The writer is sugim48.

Contest Link

Contest Announcement

Let's discuss problems after the contest.

AtCoder Grand Contest 003 will be held on Sunday (time). The writer is DEGwer.

Contest Link

Contest Announcement

Let's discuss problems after the contest.

Also, we've just announced Code Festival 2016!

We announce a new international onsite competition: Code Festival 2016. The contests will be held on AtCoder.

The top 20 foreign (non-Japanese) university students are invited to the Finals in Japan. (Even if you are not a student, you can participate in qualification rounds and parallel rounds of onsite contests. All of these contests are rated.)

The flight tickets and hotels for finalists are paid by organizers.

There will be three qualification rounds. Top 10 foreign students from round A and top 5 each from round B and C will qualify for the onsite contest.

• Round A: September 24th, 21:00 JST.
• Round B: October 10th, 13:00 JST.
• Round C: October 23rd, 21:00 JST.
• Onsite Round: November 26th-28th

Also, there will be many interesting events during the onsite competition.

More detailed information can be found at the official website.

All testcases of atcoder problems will be posted here: https://www.dropbox.com/sh/arnpe0ef5wds8cv/AAAk_SECQ2Nc6SVGii3rHX6Fa?dl=0

If you are interested in the rating system, please check rating.pdf at https://www.dropbox.com/sh/zpgcogxmmu84rr8/AADcw6o7M9tJFDgtpqEQQ46Ua?dl=0

AtCoder Grand Contest 002 will be held on Sunday (time). The writer is sugim48.

Contest Link

Contest Announcement

Let's discuss problems after the contest.

UPD: Thank you for participation. Editorial (English at the bottom)

AtCoder Grand Contest 001 will start soon (time).

Note that you need to click the blue button here to register.

Let's discuss problems after the contest.

The contest duration is changed to 110 minutes.

The contest has finished. How was the contest?

Congratulations to cgy4ever for winning!

Editorial: https://agc001.contest.atcoder.jp/data/agc/001/editorial.pdf (English is at the bottom)

UPD: The rating is updated.

Hello!

We made a new programming contest website called AtCoder. I'm the admin of AtCoder.

The first international contest called AtCoder Grand Contest 001 will be held on this Saturday (Time), and we are planning to hold a lot of contests regularly. This time the problems were written by snuke. We invite you to participate in our contests!

See AtCoder's Website for detailed information.

I was an admin of TopCoder for about 4 years. Recently I came back as a competitor and I participated in four SRMs. Here are my performances:

SRM 681 Hard: CoinFlips

It was an easy DP, but I started to implement something stupid and wasted time. When I finished coding around 5 minutes before the end of the contest, the server was slow and I couldn't compile my solution. Though the match was unrated, I should have solved it earlier.

SRM 682 Hard: TheKFactor

My solution failed because of precision errors (in Linear Programming). I should have used long doubles instead of doubles (and passed in the practice room).

SRM 683 Hard: RandomWalkOnGrid

Failed systest because of two (!) stupid mistakes: incorrect array size and integer overflow.

SRM 684 Hard: Permutant

Missed cases with a.size() == 1. Failed systest again.

It's really important to keep participating in TopCoder matches. Now I can't solve anything!

If you think the new website is difficult to use, please bookmark this post.

TopCoder Arena

Event Calendar

Rating

Editorials

Member Search

Profile

https://www.topcoder.com/members/YOUR_HANDLE_HERE/details/?track=DATA_SCIENCE&subTrack=SRM

Statistics

Match Archive

Match Results

Problem Archive

For Writers

MPSQAS

External Website (by hotpepsi)

Top Page

Profile: https://competitiveprogramming.info/topcoder/handle/YOUR_HANDLE_HERE

One day you came up with a brilliant solution during a contest, implemented it very carefully, and submitted it confidently. The verdict was ...... WA.

Probably most of you have experienced this sad situation. You can start debugging if you know the reason of WA, but what do you do otherwise? I frequently have trouble with this situation, so I'd like to ask your opinion. What should we do when we get WA?

Here are several possibilities:

1. Reread your code.

This is the simplest way of debugging. You may find some stupid typos.

2. Try various manual testcases.

Examples may not be very strong. Try some small tricky cases against your code.

3. Recheck the correctness of your algorithm.

Have you proved your solution? Is the proof correct?

4. Reread the statement.

You may have misunderstood the statement. Read it again to make sure that you understood the task correctly.

5. Stress-testing.

Write a straightforward solution, create lots of testcases by yourself, and compare both solutions. This is a very strong way to debug your solution, but time consuming.

6. Change the coder.

When you compete as a team, ask someone else to solve the problem instead.

7. Doubt the judge.

Judges are humans. They are not 100% correct.

8. Give up.

You may have other tasks to solve. Simply give up the current task and try something else.

GCJ will start in less than 24 hours.

Live Stream: https://www.youtube.com/watch?v=rh_EYIu7Ztc

Unfortunately I don't have time to edit this table, but rowdark will participate, and JoeyWheeler won't.

Participants:

Recently IMO 2015 has ended. Problem 6 was the hardest one and solved by only 11 contestants, but for competitive programmers this task wasn't that hard. If you are interested in it, I think it's worth trying even if you haven't solved any IMO problems.

The problem statement is here.

I wrote some hints in white characters.

Hint 1: How is it related to competitive programming?

Hint 2: Doesn't it look like bitmask DP?

Hint 3: Run the following program.

mask = 0;

for(i=1;;i++){

mask» = 1;

mask| = (1«(a_i - 1)); // here the newly set bit must be 0 before this operation

}

Hint 4: The number of '1' bits in mask is non-decreasing while the program is running.

So, the number of '1' bits will be constant at some moment: call it b.

Then, the sum of (a_j - b) is the difference of sum of positions of set bits in mask when i = m and i = n.

I'm currently at the airport now, and I have some free time before boarding. Here's my prediction of this year's WF:

1. SPb ITMO
2. Moscow SU
3. U Zagreb
4. Tsinghua
5. MIT
6. U Tokyo
7. U Warsaw
8. Lviv NU
9. Shanghai Jiao Tong
10. Jagiellonian
11. SPb SU
12. University of California at Berkeley

After the contest, let's see if my predictions are good :)

Among top 25 participants of round 3, 23 are in the finalists group. Here are their handles: