This year I haven't decided whether I'll participate (the flight won't be paid). Anyway, here is the top 25:

AtCoder Grand Contest 015 will be held on Saturday (time). The writer is DEGwer.

Contest Link

Contest Announcement

The point values will be announced later.

Let's discuss problems after the contest.

By the way, the writer is currently flying.

1. Tsinghua (Win: 40%, Gold: 90%, Medal: 100% after some rounding)

• CF max: 3441, 3203, 2967 (agg = 3516)
• Open Cup: 1, 1, 11, 9 (median = 5)
• China Final: 1
• MIPT: 1, 1, 1, 2, 4, 1, 4

2. Warsaw (Win: 15%, Gold: 75%, Medal: 95%)

• CF max: 3122, 2962, 2826 (agg = 3237)
• Open Cup: 2, 3 (median = 2.5)
• Petrozavodsk: 4, 2, 4, 3, 2, 2, 1, 2

3. SPb ITMO (Win: 15%, Gold: 50%, Medal: 90%)

• CF max: 2880, 2870, 2860 (agg = 3104)
• Open Cup: 7, 3, 2, 1, 13, 1, 2, 1, 3, 7, 13, 8, 8, 12, 3, 2, 1, 12 (median = 3)
• Petrozavodsk: 4, 1, 3, 1, 6, 5, 3, 7, 5
• MIPT: 6, 2, 3, 1, 5, 2, 1

4. SPb SU (Win: 10%, Gold: 40%, Medal: 85%)

• CF max: 3170, 2951, 2936 (agg = 3281)
• Open Cup: 9, 21, 18, 5, 3, 4, 9, 9, 6, 1, 2, 2, 7, 1, 4, 23, 20, 4 (median = 5.5)
• Petrozavodsk: 7, 3, 6, 5, 8, 1, 4, 5, 1
• MIPT: 2, 4, 2, 3, 1, 10, 8

5. Seoul (Win: 5%, Gold: 40%, Medal: 85%)

• CF max: 3174, 2919, 2760 (agg = 3250)
• Open Cup: 4, failed, 4 (median = 4)

6. MIPT (Win: 5%, Gold: 30%, Medal: 75%)

• CF max: 2928, 2757, 2756 (agg = 3063)
• Open Cup: 16, 29, 27, 28, 7, 24, 17, 15, 9, 15, 17, 3, 9, 4, 10 (median = 15)
• Petrozavodsk: 1, 5, 5, 5, 1, 6, 6, 1
• MIPT: 3, 6, 5, 4, 6, 3

7. MIT (Win: 5%, Gold: 30%, Medal: 75%)

• CF max: 2900, 2637, 2540 (agg = 2981)
• Open Cup: Equivalent to 2.5 in NAIPC

8. KTH (Gold: 10%, Medal: 60%)

• CF max: 2761, 2637, 2273 (agg = 2870)
• Open Cup: 2, 17, failed, 7 (median = 12)
• MIPT: 5, 5, 16, 7, 7, 2

9. Fudan (Gold: 5%, Medal: 55%)

• CF max: 2543, 2367, 2327 (agg = 2667)
• Open Cup: 6, 13, 9, 6, 13, 18 (median = 11)
• China Final: 5
• MIPT: 12, 3, 7, 15, 13, 4, 5

10. New South Wales (Gold: 5%, Medal: 50%)

• CF max: 3073, 2429, 2006 (agg = 3082)
• Open Cup: 6, 8, 16 (median = 8)
• MIPT: 14, 9, 10, 16, 2, 5, 7

11. Tokyo (Medal: 50%)

• CF max: 2762, 2694, 2424 (agg = 2903)
• Open Cup: 29, 5, 10, 12, 14, 29 (median = 13)
• MIPT: 11, 10, 6, 8, 15, 6, 6
• Barcelona: 1, 1, 1, 2, 3, 1, 1

12. SJTU (Medal: 50%)

• CF max: 2707, 2609, 2582 (agg = 2874)
• Open Cup: 26, 3, 18, failed, 21, 12, 10, 20, 26, 14 (median = 19)
• China Final: 2
• MIPT: 8, 7, 4, 10, 3, 9, 10

I won't be surprised if the following teams get a medal:

13. NTU (Medal: 45%)

• CF max: 2772, 2341, 2220 (agg = 2808)
• Open Cup: 11, 15, 21, 10, 2 (median = 11)

14. Waterloo (Medal: 45%)

• CF max: 2925, 2908, 2703 (agg = 3100)
• Open Cup: Equivalent to 12.5 in NAIPC
• Barcelona: 3, 2, 4, 1, 1, 3, 2

15. Perm SU (Medal: 40%)

• CF max: 3037, 2850, 2578 (agg = 3127)
• Open Cup: 6, 18, failed, 3, failed, 9, 18, 7, 24, 15, 14, 16, 16, 7, 21, 16, 21, 17 (median = 16)
• Petrozavodsk: 8, 12, 10, 14, 10, 10, 2, 6, 6
• MIPT: 4, 8, 11, 5, 20, 7, 9

16. Peking (Medal: 40%)

• CF max: 2920, 2566, 2338 (agg = 2965)
• Open Cup: 21, 3 (median = 12)
• China Final: 6

17. Helsinki (Medal: 35%)

• CF max: 2721, 2280, 1516 (agg = 2745)
• Open Cup: 15, failed, 9, failed, 16, 4, 17, 11, 30, 18, 2, failed, 8 (median = 16)
• Petrozavodsk: 3, 26, 25, 11, 11, 7, 10, 2, 9
• MIPT: 10, 16, 14, 6, 23, 17, 3

18. BSUIR (Medal: 30%)

• CF max: 2825, 2625, 2466 (agg = 2943)
• MIPT: 7, 13, 8, 11, 9, 13, 12

===

• Expected win of top 7 = 0.95
• Expected gold of top 10 = 3.75
• Expected medal of top 18 = 11.05

And I guess Tokyo Institute of Technology will be around 25th, Keio will be around 40th.

AtCoder Grand Contest 014 will be held on Saturday (time). The writer is yutaka1999.

Contest Link

Contest Announcement

The point values are 300 — 500 — 700 — 900 — 1400 — 2400. Note that the contest duration is unusual (130 minutes).

Let's discuss problems after the contest.

http://rng-58.blogspot.jp/2017/05/summary-of-open-cup-2016-2017.html

Let's discuss problems.

B is very nice. Until the end of the contest, I thought it was a marathon task. Then yutaka1999 told me the following: for an odd prime p, a[p] = 2 - p%4.

And I like geometry tasks like J.

There are lots of important tournaments in this season, and we moved some AtCoder contests to avoid collision. Please check https://atcoder.jp/.

We'll add more ARC/ABCs in May.

AtCoder Grand Contest 013 will be held on Saturday (time). The writer is maroonrk.

Contest Link

Contest Announcement

The point values are 300 — 500 — 700 — 900 — 1600 — 2000. Note that the contest duration is unusual (150 minutes).

Let's discuss problems after the contest.

AtCoder Grand Contest 012 will be held on Saturday (time). The writer is camypaper.

Contest Link

Contest Announcement

The point values are 300 — 700(200) — 1000 — 1000 — 1000 — 2000.

Let's discuss problems after the contest.

Let's discuss problems.

Does anyone have an idea for D?

There will be ARC 070 this Saturday, and interactive problems may be used there.

You can try an example of interactive problem on AtCoder here: https://practice.contest.atcoder.jp/tasks/practice_2

Here is my solution for 100 points:

#include <fstream>
#include <string>

using namespace std;

int main(void){
	int N,Q,i,j;
	
	scanf("%d%d", &N, &Q);
	
	string s;
	for(i=0;i<N;i++) s += (char)('A' + i);
	
	for(i=0;i<N;i++) for(j=0;j<N-1;j++){
		printf("? %c %c\n", s[j], s[j+1]);
		fflush(stdout);
		char ans;
		scanf(" %c", &ans);
		if(ans == '>') swap(s[j], s[j+1]);
	}
	
	printf("! %s\n", s.c_str());
	fflush(stdout);
	
	return 0;
}

AtCoder Grand Contest 011 will be held on Sunday (time). The writer is semiexp.

Contest Link

Contest Announcement

The point values are 300 — 400 — 800 — 900 — 1300 — 1700 (?).

Let's discuss problems after the contest.

Mujin Programming Challenge 2017 will be held on February 25th, 21:00 — 23:00 JST.

This is an online contest, and the top 30 people will be awarded prizes. The prize for the first place is $2000.

Please check the official site for details.

You will be asked to fill a questionnaire when you register, so please register at least several minutes before the contest.

UPD: Point values are 900(500) — 1300(300) — 1300 — 1800. The full scores correspond to C, D, E, F in AGC, and partial scores correspond to B, A.

If you are a contestant, you can be relaxed and you can do anything (except for cheating). It's perfectly fine if you just guess the solution and submit it without knowing why (though personally I don't find it very beautiful). However, if you are a writer, you need to prove your solution. Here is the list of things you have to prove:

1. Correctness.

Does your solution always return correct answers for all possible valid inputs?

• GOOD: Strict proof.
• BAD: My intuition tells that this is correct!
• BAD: I tried really hard to come up with counterexamples, but I couldn't. It must be correct!

2. Time Complexity.

Does your solution always run in time for all possible valid inputs?

• GOOD: It's O(n²) and the constraints say n ≤ 1000. It should work.
• GOOD: For this problem we can prove that the slowest case is xxx. Experimentally, my solution works for the input xxx under the given TL.
• BAD: I tried really hard to generate various testcases, and my solution passed all cases!

3. Randomized Algorithms.

Randomized algorithms are not hackish ways of solving problems. The writers should prove that for any valid input, the intended solution works correctly with very high probability. Please check here for an example of such proof. Another example is Rolling Hash: please check here. Note that, for example when we compute 10⁵ hashes for strings of lengths 10⁵, you need four hashes of prime modulo around 10⁹, not two. (Practically two works but we can't prove that).

4. Precision.

Especially in geometry problems, we sometimes use epsilons. However writers should be careful about the use of epsilons.

• GOOD: We know |b| and |d| are up to 10⁴. Let's use eps = 10^- 9 for comparing two fractions a / b and c / d.
• BAD: Let's use eps = 10^- 9! (without reasons)

When the intended solution uses complicated double operations (like sqrt, trigonometry, log, lots of fractions, etc.) such analysis may be hard. In this case, one possible way is to add constraints like "even if we move a point by up to 10^- 3, the answer doesn't change".

http://rng-58.blogspot.jp/2017/02/best-performance-and-worst-performance.html

AtCoder Grand Contest 010 will be held on Saturday (time). The writer is yutaka1999.

Contest Link

Contest Announcement

The point values are 300 — 500 — 700 — 1000 — 1600 — 1600.

Let's discuss problems after the contest.

My thoughts on yesterday's problem D and hashing.

http://rng-58.blogspot.jp/2017/02/hashing-and-probability-of-collision.html

http://rng-58.blogspot.jp/2017/02/january-contests.html

UPD: The contest is at https://www.facebook.com/hackercup/round/1799632126966939/.

I barely qualified, so I do this again.

AtCoder Grand Contest 009 will be held on Sunday (time). The writer is DEGwer.

Contest Link

Contest Announcement

The point values are 300 — 800 — 1100 — 1400 — 1600.

Note that the duration and the number of tasks is a bit unusual: 5 tasks in 2 hours.

Let's discuss problems after the contest.

I started a blog.

http://rng-58.blogspot.jp/

Who is this?

Sorry for late announcement, I completely forgot it.

AtCoder Grand Contest 008 will start soon! https://agc008.contest.atcoder.jp/

Hello.

I'm planning to participate in a contest tonight. This is a team contest — and unlike ICPC, there is no limit to the number of computers. So, essentially this is an individual contest, and the score of a team is defined as the union of problems solved by the team members. I'm looking for my teammates in this contest.

The problem statements are provided only in Japanese. However, don't be afraid. If you become my teammate, I will describe the problems in English. (I may also solve a few problems myself, but I'm not sure).

The contest will start at https://www.timeanddate.com/worldclock/fixedtime.html?iso=20161224T22&p1=248, and the duration of the contest is 4 hours. If you are interested in it, please reply this post until 30 minutes before the contest (that is 80 minutes from now).

This is a non-serious contest, and I won't care the rank too much — the main purpose of this contest is to have fun. Some problems may be unusual.