Hi everyone,
April Fools is near and as usual we have an April Fools Day Contest on Codeforces this year. In addition to that, I usually try to host some form of mini April Fools Contest for my friends every year (or almost every year).
This year, I am trying to host a bigger April Fools Day contest than usual and I invite everyone to participate! In view of the April Fools contest on Codeforces, the round will begin at 31 March 10pm (GMT+8) and lasts for exactly $$$24$$$ hours (and thus it will end ~35 minutes before the CF April Fools round).
The contest will consist of several unusual tasks, and I hope that everyone will at least find something interesting. The problems will not be sorted by increasing order of difficulty (if the word difficulty is even applicable), so it is highly advisable to read (and try!) all tasks. This round is not an offical Codeforces round and thus is obviously unrated.
There is a Discord server for this contest (you can join it using this link). The Discord server might be required for some tasks. Hope to see you there!
Contest Link: here
UPD: The contest is open to both individuals and teams. However, if you decide to join as part of a team, I encourage you to use the team registration feature on CF or at least submit from just one account.
I would also like to thank gamegame and Savior-of-Cross for their help in testing and feedback (which changed one of the tasks).
The contest scoring will be IOI-styled, and there are no time penalties. Most of the tasks have some form of partial scoring. There will be $$$7$$$ tasks in total, with scores $$$100-100-100-100-100-100-200$$$.
UPD 2: Registration should be open now. The contest starts in ~6 hours. Good luck and have fun! (If you haven't joined the discord server, I encourage you to do so :) ).
UPD 3: The contest has just begun! Good luck and have fun. :)
UPD 4:
Here are some statistics.
First to AC:
A: I_love_Hoang_Yen (00:07)
B: googol_S0 (03:42)
C: 244mhq + antontrygubO_o (00:46)
D: conqueror_of_tourist (00:29)
E: conqueror_of_tourist (01:58)
F: ksun48 + tourist (11:05)
G: N/A
Number of ACs for each problem
A: 45
B: 3
C: 13
D: 27
E: 17
F: 2
G: 0
Number of ACs for Hololive Subtasks
Watame Janken: 10
Friend Fubuki: 33
Mio Yacht: 2
Yandere Rushia: 15
Apex Aqua: 8
Suisei Tetris: 10
All-Rejecting Okayu: 0 (shoutout to tourist+ksun48 and Ari for being the only ones to get $$$>4$$$ points!)
Gambling Pekora: 7
Korone Game: 6
Untitled Subaru Game: 2 (madlads AMO5 and Ari)
Hall of Fame
Top Scorers (Full Score = 800)
ksun48 + tourist: 784 (only team to AC all A-F!)
Golovanov399 AndreySergunin amethyst0: 679
conqueror_of_tourist: 669
kclee2172: 618
googol_S0: 592
Maksim1744: 592
I_love_Hoang_Yen: 556
dorijanlendvaj: 500
ymmparsa Arian.Eft: 500
Ari: 499 (highest score in G!)
Short Hints for all problems
A. Pacman and Power Pellet The map has similar properties with the map in the game Pacman.
B. As Easy As ABC Easy and ABC both hints "Atcoder Beginner Contest". This is confirmed by the weird output format.
C. Two Hashes It is possible to achieve over 99.99% success rate. The trick is that $$$115381398^3 \equiv 1 \pmod{10^{9}+9}$$$.
D. Math Homework Figure out what each function is. Use Python eval.
Code E. Simple Exercise There are probably many solutions. My solution is that there exists enough solutions using 5 distinct numbers, where the largest 4 numbers used are large (e.g. one solution uses the numbers $$$528,952,971,972,999$$$). You can write a simple brute force and run locally until you have enough solutions.
F. Mystery Task 2 Quadratic Residues
Task 3 Japanese verbs in te form.
Task 4 If you solved this, congrats you got Rick Rolled.
Task 5 The pattern is a bit like Fibonacci. The inputted number is the number of times you iterate the recurrence relation. $$$0$$$ resets the entire thing to default state.
G. Can you do the hololive? Watame Janken There is a task from Untitled Subaru Game that asks you to win 12 times in a row. Hence, there must be an exploit. The key exploit is that the sequence of moves is periodic (with period 21, which is slightly long, so you might need to figure out that this task requires cheating to solve it).
Friend Fubuki No catch here, just make 10 friends.
Mio Yacht No catch here, just play the game.
Yandere Rushia How this task works is that affection value decreases by 1% every 5 minutes. Every pat/date command increases the affection value by some %, which increases as you answer more quiz questions correctly.
Apex Aqua No catch here, just play the game.
Suisei Tetris No catch here, just play the game.
All-Rejecting Okayu Your task is to find 10 hidden 9-digit numbers. The aha is that each of the 10 characters in this problem has a 9-digit number "hidden" in their task!
Hidden Numbers Watame It's the 9-digit number written in the Watame section of the documentation of the bot.
Fubuki It's hidden in Fubuki's picture.
Mio It's the 9-digit "ID" written at the footer of every Yacht game.
Rushia The number of exclamation marks when you use the pat command is periodic modulo $$$9$$$. They form the digits of a 9-digit number.
Aqua The initial announcement in the Discord group has a sample usage of Aqua's h!hp command. It is shown there "The enemy was last killed by a facade." (where a facade is replaced by the previous killer after the game has started). Convert afacade from hexadecimal to get a 9-digit number.
Suisei The answer is 123456789, written on the bottom row of the Tetris grid. You might have also guessed this number without knowing the reason.
Okayu Every 4 rejections will prompt a hint message from Okayu. Once you gather all 5 hint messages, you can write a code to find the only number that satisfies all 5 criterion.
Pekora Hidden in the message shown when you use the beg command. The positions of the bolded letters in the sentence gives the 9-digit number.
Korone Hidden in the name of the 3 "enemies" you fight in the 3 levels as Japanese wordplay. The first level is Sherlock (しゃろく) (which sounds like 4869 in Japanese), second level is Ichigo (Ichi-go = 15) and third level is Korosan (563).
Subaru If you read the initial letters of all the $$$10$$$ tasks, you will see that it spells 12 FACTORIAL. So the answer is $$$12!$$$, which happens to have $$$9$$$ digits.
Gambling Pekora No catch here except that blackjack odds are slightly modified. One idea is to spam high-risk high-reward gambles early and abuse the beg feature when you fail until you gained a decent amount. Then, after you get somewhat close (say few times below) the goal, you can try to do safer bets.
Korone Game Level 1 Long words kill you.
Level 2 Shuffle icon: Outputs the odd-positioned digits first before the even-positioned digits.
7 o'clock icon: Appends the digit 7.
No under 18 allowed icon: Deletes all occurrences of the substring 18.
Mystery icon: Split the number into 2 roughly equal parts, and add the two parts together.
Level 3 You can take a few tries to plot out the map, then the rest is trivial.
Untitled Subaru Game No catch here, just complete the checklist.
I have participated in another april fools type contest by zscoder and it was quite cool. The best part was a person spoiling the solution to an unsolved problem in a discord chat without reading it. Looking forward to participating in this one too.
hardest problem unsolved in a contest, must be geometry
Auto comment: topic has been updated by zscoder (previous revision, new revision, compare).
Thanks :)
:D
Auto comment: topic has been updated by zscoder (previous revision, new revision, compare).
.
Auto comment: topic has been updated by zscoder (previous revision, new revision, compare).
Why so many people (including me) got 0 points in problem A, despite an easy problem :((
I think the fact of it was that if u are in the first row and go up u will go to the bottom row just like the actual game. (I’m saying this cause at first we didn’t pay attention to this and got a wrong answer.)
Yep, that's the joke for this problem.
Auto comment: topic has been updated by zscoder (previous revision, new revision, compare).
Thanks a lot for hosting the contest! It was really fun even though I missed dumb stuff and I suck at Tetris lol