Hello, Codeforces!

On May 5th, 21:00 JST, AtCoder Beginner Contest 096 will be held.

The problems were prepared by square1001 and me (E869120). Thank you for chokudai, rng_58, evima to helping us to host the round on AtCoder!

You will be given **100 minutes** and there are **4 problems** with following scores: 100 — 200 — 300 — 400.

This contest is **rated** for all participants whose rating is less than 1200, but as usual, participants whose rating is more or equal to 1200 can take part out of competition.

Good luck and have fun!

##### UPDATE

- The contest will start in
**less than a day**. - The contest is over! Thank you for your participation! Let's discuss about the problems.
- Editorial is out! Link

I'm looking forward to participating the contest! Actually, the last time they held ABC was 18th February, but I couldn't take part in. On a personal note, E869120 is the person who pulled me into the world of competitive programming, and I really appreciate it. BTW, I hope my rating will be increased.

Good Luck and Have Fun!

Auto comment: topic has been updated by E869120 (previous revision, new revision, compare).Will the theme be Children's Day?

!! Reminder: The contest starts in 4 hours :-) !!

Problem D was fun! Liked solving it. :)

Auto comment: topic has been updated by E869120 (previous revision, new revision, compare).Problem D really nice :D

Very nice contest and problem D was especially elegant ! What was the inspiration for it ? Was it taken from some Math contest ?

Here is the GitHub of all my codes.

Here is the Quora Blog post about problem D.

In fact, at first I wanted to set problem D constructive problem. Then, I thought 15 minutes. I thought "It is good to make problem about prime and composite numbers for ABC-D". Actually I wrote 4 ABCs, so I should know what problem is good for ABC. Finally, after thinking 40 minutes, I came up with the problem.

Great work ! This was the first AtCoder contest where I upsolved all 4 problems !

I love constructive problems.

Did you notice any other solutions ?

I misread problem D (thought the sum of the whole array had to be composite) because I skimmed it, gave up on finding the bug, then realized after contest my solution was basically the same idea as editorial but I solved a different problem.

RIP

What was your solution ?

OK. I thought it was the whole array not 5 elements.

Mod 2 Solution only works for evens, so I did the next easiest thing: mod 3.

if n mod 3 = 0 loop through primes in the sequence 4, 7, 10 (mod 3 = 1)

n mod 3 = 1, print out 3 (which is 0 mod 3), then do the same strategy as above

n mod 3 = 2 print out 2, then do same strategy as above

Sum will always be multiple of three.

The idea is the same as tutorial: if you have n items how to add them so they are divisible by k, well you just add then so that x mod k == 1 is n is divisible by k. And you use an offset otherwise (since everything was 5 you didn't have to).

I just went back to sleep after submitting problems, so I didn't check if any of them were right (and thus I was surprised when I got the problem wrong)

E869120

This case is not handled in Problem C

1 1

#

This is my submission and got accepted and I didn't handle this Case

https://abc096.contest.atcoder.jp/submissions/2470447

Expected answer is "No" ?

Yes , expected answer is "No".

Oh, no. I made the testcase of problem C, so it's my mistake that I didn't made such simple testcase. I thought that I made some corner cases, but I only concentrated to make "maximal cases" for corner case one, so we should definitely make "minimal cases". I will be aware of it next time.