Hi everyone,↵
↵
April Fools is near and as usual we have an [April Fools Day Contest](https://mirror.codeforces.com/blog/entry/88840) 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)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=April+Fools+Day+Contest+2021+%28ZS%29&iso=20210331T22&p1=122) 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](https://discord.gg/DAKHuRJ4Yb)). **The Discord server might be required for some tasks.** Hope to see you there!↵
↵
Contest Link: [here](https://mirror.codeforces.com/contestInvitation/afc425fa40020871454f12eb9cb750812e93e98c)↵
↵
**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 [user:gamegame,2021-03-30] and [user:DreamingLeaf,2021-03-30] 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,2021-04-01 (00:07)↵
↵
B: ~googol_S0,2021-04-01 (03:42)↵
↵
C: ~kefaa2,2021-04-01 + ~antontrygubO_o,2021-04-01 (00:46)↵
↵
D: ~conqueror_of_tourist,2021-04-01 (00:29)↵
↵
E: ~conqueror_of_tourist,2021-04-01 (01:58)↵
↵
F: ~ksun48,2021-04-01 + ~tourist,2021-04-01 (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 [user:tourist,2021-04-01]+[user:ksun48,2021-04-01] and [user:Ari,2021-04-01] for being the only ones to get $>4$ points!)↵
↵
Gambling Pekora: 7 ↵
↵
Korone Game: 6↵
↵
Untitled Subaru Game: 2 (madlads [user:AMO5,2021-04-01] and [user:Ari,2021-04-01])↵
↵
Hall of Fame↵
------------------↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
Top Scorers (Full Score = 800)↵
------------------------------↵
↵
1. ~ksun48,2021-04-01 + ~tourist,2021-04-01: 784 (only team to AC all A-F!)↵
↵
2. ~Golovanov399,2021-04-01 ~AndreySergunin,2021-04-01 ~amethyst0,2021-04-01: 679↵
↵
3. ~conqueror_of_tourist,2021-04-01: 669↵
↵
4. ~kclee2172,2021-04-01: 618↵
↵
5. ~googol_S0,2021-04-01: 592↵
↵
5. ~Maksim1744,2021-04-01: 592↵
↵
7. ~I_love_Hoang_Yen,2021-04-01: 556↵
↵
8. ~dorijanlendvaj,2021-04-01: 500↵
↵
8. ~Parsa84,2021-04-01 [user:Arian.Eft,2021-04-01]: 500↵
↵
10. ~Ari,2021-04-01: 499 (highest score in G!)↵
↵
Short Hints for all problems↵
----------------------------↵
↵
<spoiler summary="A. Pacman and Power Pellet">↵
The map has similar properties with the map in the game Pacman. ↵
↵
<spoiler summary="B. As Easy As ABC">↵
Easy and ABC both hints "Atcoder Beginner Contest". This is confirmed by the weird output format.↵
↵
<spoiler summary="C. Two Hashes">↵
It is possible to achieve over 99.99% success rate. The trick is that $115381398^3 \equiv 1 \pmod{10^{9}+9}$.↵
↵
<spoiler summary="D. Math Homework">↵
Figure out what each function is. Use Python eval.↵
[Code](https://ideone.com/812DxQ)↵
↵
<spoiler summary="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.↵
↵
<spoiler summary="F. Mystery">↵
<spoiler summary="Task 1">↵
$a+b$↵
</spoiler>↵
<br>↵
<spoiler summary="Task 2">↵
Quadratic Residues↵
</spoiler>↵
<br>↵
<spoiler summary="Task 3">↵
Japanese verbs in te form.↵
</spoiler>↵
<br>↵
<spoiler summary="Task 4">↵
If you solved this, congrats you got Rick Rolled.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
</spoiler> ↵
↵
<spoiler summary="G. Can you do the hololive?">↵
<spoiler summary="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).↵
</spoiler>↵
<br>↵
<spoiler summary="Friend Fubuki">↵
No catch here, just make 10 friends.↵
</spoiler>↵
<br>↵
<spoiler summary="Mio Yacht">↵
No catch here, just play the game.↵
</spoiler>↵
<br>↵
<spoiler summary="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. ↵
</spoiler>↵
<br>↵
<spoiler summary="Apex Aqua">↵
No catch here, just play the game.↵
</spoiler>↵
<br>↵
<spoiler summary="Suisei Tetris">↵
No catch here, just play the game.↵
</spoiler>↵
<br>↵
<spoiler summary="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! ↵
<spoiler summary="Hidden Numbers">↵
<spoiler summary="Watame">↵
It's the 9-digit number written in the Watame section of the documentation of the bot.↵
</spoiler>↵
<br>↵
<spoiler summary="Fubuki">↵
It's hidden in Fubuki's picture.↵
</spoiler>↵
<br>↵
<spoiler summary="Mio">↵
It's the 9-digit "ID" written at the footer of every Yacht game.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br> ↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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). ↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler> ↵
</spoiler>↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler> ↵
<br>↵
<spoiler summary="Korone Game">↵
<spoiler summary="Level 1">↵
Long words kill you.↵
</spoiler> ↵
<br>↵
<spoiler summary="Level 2">↵
Shuffle icon: Outputs the odd-positioned digits first before the even-positioned digits.↵
<br>↵
7 o'clock icon: Appends the digit 7.↵
<br>↵
No under 18 allowed icon: Deletes all occurrences of the substring 18.↵
<br>↵
Mystery icon: Split the number into 2 roughly equal parts, and add the two parts together.↵
</spoiler> ↵
<br>↵
<spoiler summary="Level 3">↵
You can take a few tries to plot out the map, then the rest is trivial.↵
</spoiler> ↵
</spoiler>↵
<br>↵
<spoiler summary="Untitled Subaru Game">↵
No catch here, just complete the checklist.↵
</spoiler>↵
</spoiler>
↵
April Fools is near and as usual we have an [April Fools Day Contest](https://mirror.codeforces.com/blog/entry/88840) 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)](https://www.timeanddate.com/worldclock/fixedtime.html?msg=April+Fools+Day+Contest+2021+%28ZS%29&iso=20210331T22&p1=122) 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](https://discord.gg/DAKHuRJ4Yb)). **The Discord server might be required for some tasks.** Hope to see you there!↵
↵
Contest Link: [here](https://mirror.codeforces.com/contestInvitation/afc425fa40020871454f12eb9cb750812e93e98c)↵
↵
**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 [user:gamegame,2021-03-30] and [user:DreamingLeaf,2021-03-30] 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,2021-04-01 (00:07)↵
↵
B: ~googol_S0,2021-04-01 (03:42)↵
↵
C: ~kefaa2,2021-04-01 + ~antontrygubO_o,2021-04-01 (00:46)↵
↵
D: ~conqueror_of_tourist,2021-04-01 (00:29)↵
↵
E: ~conqueror_of_tourist,2021-04-01 (01:58)↵
↵
F: ~ksun48,2021-04-01 + ~tourist,2021-04-01 (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 [user:tourist,2021-04-01]+[user:ksun48,2021-04-01] and [user:Ari,2021-04-01] for being the only ones to get $>4$ points!)↵
↵
Gambling Pekora: 7 ↵
↵
Korone Game: 6↵
↵
Untitled Subaru Game: 2 (madlads [user:AMO5,2021-04-01] and [user:Ari,2021-04-01])↵
↵
Hall of Fame↵
------------------↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
↵
Top Scorers (Full Score = 800)↵
------------------------------↵
↵
1. ~ksun48,2021-04-01 + ~tourist,2021-04-01: 784 (only team to AC all A-F!)↵
↵
2. ~Golovanov399,2021-04-01 ~AndreySergunin,2021-04-01 ~amethyst0,2021-04-01: 679↵
↵
3. ~conqueror_of_tourist,2021-04-01: 669↵
↵
4. ~kclee2172,2021-04-01: 618↵
↵
5. ~googol_S0,2021-04-01: 592↵
↵
5. ~Maksim1744,2021-04-01: 592↵
↵
7. ~I_love_Hoang_Yen,2021-04-01: 556↵
↵
8. ~dorijanlendvaj,2021-04-01: 500↵
↵
8. ~Parsa84,2021-04-01 [user:Arian.Eft,2021-04-01]: 500↵
↵
10. ~Ari,2021-04-01: 499 (highest score in G!)↵
↵
Short Hints for all problems↵
----------------------------↵
↵
<spoiler summary="A. Pacman and Power Pellet">↵
The map has similar properties with the map in the game Pacman. ↵
↵
<spoiler summary="B. As Easy As ABC">↵
Easy and ABC both hints "Atcoder Beginner Contest". This is confirmed by the weird output format.↵
↵
<spoiler summary="C. Two Hashes">↵
It is possible to achieve over 99.99% success rate. The trick is that $115381398^3 \equiv 1 \pmod{10^{9}+9}$.↵
↵
<spoiler summary="D. Math Homework">↵
Figure out what each function is. Use Python eval.↵
[Code](https://ideone.com/812DxQ)↵
↵
<spoiler summary="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.↵
↵
<spoiler summary="F. Mystery">↵
<spoiler summary="Task 1">↵
$a+b$↵
</spoiler>↵
<br>↵
<spoiler summary="Task 2">↵
Quadratic Residues↵
</spoiler>↵
<br>↵
<spoiler summary="Task 3">↵
Japanese verbs in te form.↵
</spoiler>↵
<br>↵
<spoiler summary="Task 4">↵
If you solved this, congrats you got Rick Rolled.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
</spoiler> ↵
↵
<spoiler summary="G. Can you do the hololive?">↵
<spoiler summary="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).↵
</spoiler>↵
<br>↵
<spoiler summary="Friend Fubuki">↵
No catch here, just make 10 friends.↵
</spoiler>↵
<br>↵
<spoiler summary="Mio Yacht">↵
No catch here, just play the game.↵
</spoiler>↵
<br>↵
<spoiler summary="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. ↵
</spoiler>↵
<br>↵
<spoiler summary="Apex Aqua">↵
No catch here, just play the game.↵
</spoiler>↵
<br>↵
<spoiler summary="Suisei Tetris">↵
No catch here, just play the game.↵
</spoiler>↵
<br>↵
<spoiler summary="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! ↵
<spoiler summary="Hidden Numbers">↵
<spoiler summary="Watame">↵
It's the 9-digit number written in the Watame section of the documentation of the bot.↵
</spoiler>↵
<br>↵
<spoiler summary="Fubuki">↵
It's hidden in Fubuki's picture.↵
</spoiler>↵
<br>↵
<spoiler summary="Mio">↵
It's the 9-digit "ID" written at the footer of every Yacht game.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br> ↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler>↵
<br>↵
<spoiler summary="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). ↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler> ↵
</spoiler>↵
</spoiler>↵
<br>↵
<spoiler summary="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.↵
</spoiler> ↵
<br>↵
<spoiler summary="Korone Game">↵
<spoiler summary="Level 1">↵
Long words kill you.↵
</spoiler> ↵
<br>↵
<spoiler summary="Level 2">↵
Shuffle icon: Outputs the odd-positioned digits first before the even-positioned digits.↵
<br>↵
7 o'clock icon: Appends the digit 7.↵
<br>↵
No under 18 allowed icon: Deletes all occurrences of the substring 18.↵
<br>↵
Mystery icon: Split the number into 2 roughly equal parts, and add the two parts together.↵
</spoiler> ↵
<br>↵
<spoiler summary="Level 3">↵
You can take a few tries to plot out the map, then the rest is trivial.↵
</spoiler> ↵
</spoiler>↵
<br>↵
<spoiler summary="Untitled Subaru Game">↵
No catch here, just complete the checklist.↵
</spoiler>↵
</spoiler>
