[A — Captcha](https://codeforces.me/gym/106452/problem/A) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
Just print the number of circles in the image. There are `7` if you include the circles in `i` and `?`.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:1,a] Best Problem Ever ↵
- [likes:1,b] Incredible Problem↵
- [likes:1,c] Amazing Problem↵
- [likes:1,d] Great Problem↵
- [likes:1,e] Good Problem↵
</spoiler>↵
↵
[B — Right or Wrong?](https://codeforces.me/gym/106452/problem/B) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Solution">↵
The title implies that you should check if the 3 numbers are "right" or not. You can do this by checking that $a$, $b$, and $c$ form the side lengths of a right triangle, with $c$ as the hypotenuse.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:2,a] Best Problem Ever ↵
- [likes:2,b] Incredible Problem↵
- [likes:2,c] Amazing Problem↵
- [likes:2,d] Great Problem↵
- [likes:2,e] Good Problem↵
</spoiler>↵
↵
[C — New Sorting Algorithm](https://codeforces.me/gym/106452/problem/C) ↵
Author: [user:ChiMasterBing,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
You are sorting a permutation, so all you have to do is print out the integers from $1$ to $n$, inclusive. The time constraints are very lax for this. Though you should be careful of the memory limit. If you read the second line entirely, you will probably get MLE. If you form a large string and then print it out, you will probably get MLE.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:3,a] Best Problem Ever ↵
- [likes:3,b] Incredible Problem↵
- [likes:3,c] Amazing Problem↵
- [likes:3,d] Great Problem↵
- [likes:3,e] Good Problem↵
</spoiler>↵
↵
[D — Subset Sums](https://codeforces.me/gym/106452/problem/D) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
<spoiler summary="Hint 1">↵
Clearly, solving this problem as is is too hard. Is there anything that you are missing here?↵
</spoiler>↵
↵
↵
<spoiler summary="Hint 2">↵
Try pressing Ctrl+A to highlight all the text.↵
</spoiler>↵
↵
↵
<spoiler summary="Solution">↵
If you highlight the space below "Notes," you will see the following equations:↵
↵
↵
If you plot these functions in Desmos, you will realize that $a$ is still a variable. By setting $a$ to $0$, $1$, and $2$, you will see the equations spell out `XOR`.↵
↵
This signifies that the question is actually asking about how many subset XOR sums equal $k$. This can be done in $O(n\log \max{a_i})$↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:4,a] Best Problem Ever ↵
- [likes:4,b] Incredible Problem↵
- [likes:4,c] Amazing Problem↵
- [likes:4,d] Great Problem↵
- [likes:4,e] Good Problem↵
</spoiler>↵
↵
[E — Gemini](https://codeforces.me/gym/106452/problem/E) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
Castor and Pollux are the twin stars of the Gemini constellation, but it seems like we can only see Castor...↵
↵
<spoiler summary="Step 1">↵
To solve Castor's problem, all even numbers must be put into separate sets. It can be shown that the required number of sets is always equal to $\lfloor\frac{n}{2}\rfloor$. You can do this by pairing `1 2`, `3 4`, `5 6`, etc. for even values of $n$. If $n$ is odd, you can instead do `n-2 n-1 n` for the last set.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 1.5">↵
After submitting, you will receive a verdict of `Хороший! Now help solve Pollux's problem!` This signifies that you should now look at Castor's partner, Pollux, since he also has a problem to solve. This can be done by switching your language to Russian.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 2">↵
To solve Pollux's problem, just write any sieve to print out the primes up to $n$.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 2.5">↵
At this point, you will probably get a verdict of `Oops, now Castor is getting a Wrong Answer on his end.` This means you should somehow solve both of their problems at the same time. (This is where the weird output format comes into play)↵
</spoiler>↵
↵
↵
<spoiler summary="Step 3">↵
To solve both of their problems, first print out all of the primes in one set to satisfy Pollux's problem. Then, try to complete the original construction from Castor's problem, but skip over any instance where you have already placed a number into the set of primes. Also, place $1$ into any set other than the first set.↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:5,a] Best Problem Ever ↵
- [likes:5,b] Incredible Problem↵
- [likes:5,c] Amazing Problem↵
- [likes:5,d] Great Problem↵
- [likes:5,e] Good Problem↵
</spoiler>↵
↵
[F — Something's Fishy](https://codeforces.me/gym/106452/problem/F) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
This problem has the exact same name as [a previous UTPC April Fools problem](https://codeforces.me/gym/105071/problem/E), and it also has some cursed numbers in it, though this time it relates to a different fish.↵
↵
<spoiler summary="Solution">↵
↵
<spoiler summary="Step 1">↵
First, we should solve for the variables. ↵
$X = 2206$ ↵
$a = 14$, this should include the one that just happened before this contest ↵
$r = 3$, no the answer is not $2$, are you an AI model? ↵
$c = 37$, a reference to [this video](https://www.youtube.com/watch?v=d6iQrh2TK98) ↵
$l = 1$, this is [Legendre's Constant](https://en.wikipedia.org/wiki/Legendre%27s_constant) ↵
$j = 31$, July always has $31$ days ↵
$h = 11$, there are $9$ [Heegner numbers](https://en.wikipedia.org/wiki/Heegner_number), and $11$ is the median of all of them ↵
$m = 777$, [Matikanefukukitaru](https://gametora.com/umamusume/characters/105601-matikanefukukitaru) has a skill that activates with $777$m left in the race, she is also closely related to luck in general (and so is $777$)↵
↵
Note that the $|$ operator denotes concatenation.↵
↵
So, $Y = 143\cdot (37+10)\cdot 131\cdot 11777 \mod 10^9+7$, which gives us $Y=369071357$.↵
↵
Now, what can we do with $2206$ and $369071357$?↵
</spoiler>↵
↵
<spoiler summary="Step 1.5">↵
If you pay attention to the flavor text, it mentions something about the ICPC Championship in Asia, which is on Codeforces, and is quite recent. If you click into the contest and look at the URL, the ID of the contest is also $2206$, so what about $369071357$?↵
</spoiler>↵
↵
<spoiler summary="Step 2">↵
If you look at submission $369071357$ from the 2026 Asia Pacific Championship, you will get [this submission](https://codeforces.me/contest/2206/submission/369071357).↵
</spoiler>↵
↵
<spoiler summary="Step 3">↵
Looking at the code, it is a compile error, which is very suspicious, and there is a massive template, which is not immediately suspicious. That is, until you realize that some parts of the template are quite suspect, such as `#define N number`. When would that ever be useful? If you take all of the suspicious parts and read the capital letters in order, they will spell `ANSHIDDEN`, which should tell you that the answer is `HIDDEN`.↵
↵
<spoiler summary="Tip">↵
You can diff the submission against a previous submission to see what got changed.↵
</spoiler>↵
↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:6,a] Best Problem Ever ↵
- [likes:6,b] Incredible Problem↵
- [likes:6,c] Amazing Problem↵
- [likes:6,d] Great Problem↵
- [likes:6,e] Good Problem↵
</spoiler>↵
↵
[G — Forgot where I took this pic](https://codeforces.me/gym/106452/problem/G) ↵
Author: [user:zmonster8,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
Play Geoguessr. Any coordinate within 110 meters will be accepted. The real location is at `22.2763644 114.1568149`. You can also try to triangulate the spot since the checker will tell you how far you are.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:7,a] Best Problem Ever ↵
- [likes:7,b] Incredible Problem↵
- [likes:7,c] Amazing Problem↵
- [likes:7,d] Great Problem↵
- [likes:7,e] Good Problem↵
</spoiler>↵
↵
[H — Fill in the Blanks](https://codeforces.me/gym/106452/problem/H) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Hint">↵
It seems like increasing the index decreases the value, and decreasing the index increases the value. Also, the first element is "bad" for some reason.↵
</spoiler>↵
↵
↵
<spoiler summary="Solution">↵
You should not interpret $a_i$ as the $i$th element of a list. Rather, you should think of $a_i$ as some value $a$ in base $i$. This matches the ideas from the previous hint, and base 1 is not well defined. So the problem is simply to convert $a$ from base $i$ to base $j$. The constraints imply that the true value of $a$ does not exceed $10^{18}$. $j$ is always at most $10$, so the answer will always be numeric.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:8,a] Best Problem Ever ↵
- [likes:8,b] Incredible Problem↵
- [likes:8,c] Amazing Problem↵
- [likes:8,d] Great Problem↵
- [likes:8,e] Good Problem↵
</spoiler>↵
↵
[I — Networking Problem](https://codeforces.me/gym/106452/problem/I) ↵
Author: [user:25huangvictoria,2026-04-02]↵
↵
<spoiler summary="Solution">↵
If you submit anything, you will get a verdict of `Connection request pending. Have you checked the 6th floor?` Checking the 6th floor of the GDC will lead you to a QR code that will link to a LinkedIn profile. Connecting will give back an automated response telling you that the answer is: `I have added Victoria Huang on LinkedIn!`. (Please don't spam)↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:9,a] Best Problem Ever ↵
- [likes:9,b] Incredible Problem↵
- [likes:9,c] Amazing Problem↵
- [likes:9,d] Great Problem↵
- [likes:9,e] Good Problem↵
</spoiler>↵
↵
[J — Guess the Number!](https://codeforces.me/gym/106452/problem/J) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Solution">↵
At first, this seems impossible, until you realize that you have $4!=24$ queries, not $4$. For $1\le x\le 10^6$, binary searching on the answer will need $20$ queries, so $24$ is more than enough.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:10,a] Best Problem Ever ↵
- [likes:10,b] Incredible Problem↵
- [likes:10,c] Amazing Problem↵
- [likes:10,d] Great Problem↵
- [likes:10,e] Good Problem↵
</spoiler>↵
↵
[K — Guessing Game](https://codeforces.me/gym/106452/problem/K) ↵
Author: [user:walrusramen21,2026-04-02]↵
↵
<spoiler summary="Solution">↵
↵
<spoiler summary="Step 1">↵
After looking at the clues, you should realize that the answers cannot really be words. Each clue should solve to a year instead, but years have $4$ digits, and this game of Wordle has $5$ blanks...↵
</spoiler>↵
↵
↵
<spoiler summary="Step 2">↵
The hint says that `The present is built upon the results of the past.` This implies that you should look at the "results of the past," specifically the [past Wordle answers.](https://www.fiveforks.com/wordle/)↵
↵
You should get: ↵
1. 1646 $\rightarrow$ QUILT ↵
2. 1612 $\rightarrow$ CLAMP ↵
3. 1578 $\rightarrow$ FORUM ↵
4. 1596 $\rightarrow$ MOTEL ↵
↵
So, the final answer should be `MAUVE`.↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:11,a] Best Problem Ever ↵
- [likes:11,b] Incredible Problem↵
- [likes:11,c] Amazing Problem↵
- [likes:11,d] Great Problem↵
- [likes:11,e] Good Problem↵
</spoiler>↵
↵
[L — MST](https://codeforces.me/gym/106452/problem/L) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Solution">↵
This would require some code if this were an actual MST problem, but of course, it is not. Note that the question does not specify that the graph must be connected, so we can just choose to take none of the edges (also, all edges have positive weight). This means the answer is just always `0`.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:12,a] Best Problem Ever ↵
- [likes:12,b] Incredible Problem↵
- [likes:12,c] Amazing Problem↵
- [likes:12,d] Great Problem↵
- [likes:12,e] Good Problem↵
</spoiler>↵
↵
[M — META](https://codeforces.me/gym/106452/problem/M) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
This metapuzzle is in the style of a [puzzlehunt](https://blog.vero.site/post/puzzlehunts).↵
↵
<spoiler summary="Clues by problem">↵
↵
<spoiler summary="A">↵
Alternative medicine focused on specific points on the body using one's hands (11)↵
</spoiler>↵
↵
↵
<spoiler summary="B">↵
Something you "pass in", or an altercation (8)↵
</spoiler>↵
↵
↵
<spoiler summary="C">↵
Something you can do with a car, or something you can "catch" (5)↵
</spoiler>↵
↵
↵
<spoiler summary="D">↵
Stereotypically found in cartoons when someone is running very fast (4 5)↵
</spoiler>↵
↵
↵
<spoiler summary="E">↵
Guard, or someone who refrains from disclosing the location of their favorite restaurant (10)↵
</spoiler>↵
↵
↵
<spoiler summary="F">↵
Certain type of lounge for smoking (6)↵
</spoiler>↵
↵
↵
<spoiler summary="G">↵
Symbol representing ejection in a match (3 4)↵
</spoiler>↵
↵
↵
<spoiler summary="H">↵
Type of competition used in the Olympics that allows for second chances (9)↵
</spoiler>↵
↵
↵
<spoiler summary="I">↵
Common type of appetizer for those who cannot choose just one item (7)↵
</spoiler>↵
↵
↵
<spoiler summary="J">↵
Common action in Minecraft, or a type of fish (5)↵
</spoiler>↵
↵
↵
<spoiler summary="K">↵
Something found in grandparents' homes, or something found behind certain windows (9)↵
</spoiler>↵
↵
↵
<spoiler summary="L">↵
Alice's location (10)↵
</spoiler>↵
↵
</spoiler>↵
↵
↵
<spoiler summary="Solution">↵
You should solve all of the clues first.↵
↵
<spoiler summary="Answers to clues">↵
The parentheses indicate the enumeration of the answer to a clue. So "fish" would be (4) and "magic carp" would be (5 4) ↵
Also, after solving some of the clues, you will probably realize that all of the answers are in alphabetical order.↵
↵
<spoiler summary="A">↵
`ACUPRESSURE`↵
</spoiler>↵
↵
↵
<spoiler summary="B">↵
`ARGUMENT`, you pass in arguments in code, and get into arguments as an altercation↵
</spoiler>↵
↵
↵
<spoiler summary="C">↵
`DRIFT`, you can drift in a car, and you can catch someone's drift↵
</spoiler>↵
↵
↵
<spoiler summary="D">↵
`DUST CLOUD`↵
</spoiler>↵
↵
↵
<spoiler summary="E">↵
`GATEKEEPER`, this is modern parlance↵
</spoiler>↵
↵
↵
<spoiler summary="F">↵
`HOOKAH`, search up "hookah lounge"↵
</spoiler>↵
↵
↵
<spoiler summary="G">↵
`RED CARD`↵
</spoiler>↵
↵
↵
<spoiler summary="H">↵
`REPECHAGE`, this is used primarily in [Olympics wrestling](https://www.olympics.com/en/news/what-is-repechage-rules)↵
</spoiler>↵
↵
↵
<spoiler summary="I">↵
`SAMPLER`↵
</spoiler>↵
↵
↵
<spoiler summary="J">↵
`SMELT`, furnaces smelt in Minecraft, smelt is also a fish: https://en.wikipedia.org/wiki/Smelt_(fish)↵
</spoiler>↵
↵
↵
<spoiler summary="K">↵
`WALLPAPER`, wallpaper is found in older homes, and it is also what is behind windows (or tabs) on a computer↵
</spoiler>↵
↵
↵
<spoiler summary="L">↵
`WONDERLAND`↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Step 0.5">↵
"Undirected acyclic connected graph" just means "tree," so this puzzle should be about trees somehow. There is also mention of "trim[ming]" the trees.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 1">↵
If we "trim" some of the answers, we can see some trees show up, though they might be anagrammed. As an example, trimming WALLPAPER gives us LPAPE. Anagramming this gives us APPLE.↵
↵
<spoiler summary="Trees after trimming">↵
ACUPRESSURE $\rightarrow$ SPRUCE ↵
ARGUMENT $\rightarrow$ GUM ↵
DRIFT $\rightarrow$ FIR ↵
DUST CLOUD $\rightarrow$ LOCUST ↵
GATEKEEPER $\rightarrow$ TEAK ↵
HOOKAH $\rightarrow$ OAK ↵
RED CARD $\rightarrow$ CEDAR ↵
REPECHAGE $\rightarrow$ PEACH ↵
SAMPLER $\rightarrow$ MAPLE ↵
SMELT $\rightarrow$ ELM ↵
WALLPAPER $\rightarrow$ APPLE ↵
WONDERLAND $\rightarrow$ ALDER ↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Step 2">↵
Now that we have a list of trees, we should consider what the `1. [5] -> 8` stuff means. Usually, [5] indicates that we extract the 5th letter from some word/phrase. But the second row wants us to extract the 5th letter from GUM, which doesn't exist. So, let's sort the trees in alphabetical order, then perform the extraction.↵
↵
<spoiler summary="Extracted letters">↵
ALDER $\rightarrow$ R ↵
APPLE $\rightarrow$ E ↵
CEDAR $\rightarrow$ ED ↵
ELM $\rightarrow$ E ↵
FIR $\rightarrow$ FR ↵
GUM $\rightarrow$ U ↵
LOCUST $\rightarrow$ S ↵
MAPLE $\rightarrow$ PE ↵
OAK $\rightarrow$ O ↵
PEACH $\rightarrow$ H ↵
SPRUCE $\rightarrow$ UC ↵
TEAK $\rightarrow$ T ↵
</spoiler>↵
↵
</spoiler>↵
↵
↵
<spoiler summary="Step 3">↵
The letters we have so far don't make any sense, so let's use the information to the right of the arrows (the 8 from `1. [5] -> 8`). Looking at all of these numbers, we see that they form a permutation of the first 16 positive integers, so let's use those numbers as indices into a 16-letter phrase. Then, we can rearrange the letters we have so far to uncover `USETHEPRUFERCODE` ("use the prufer code", which [relates to trees](https://en.wikipedia.org/wiki/Pr%C3%BCfer_sequence)!). This matches up with the final answer being 4 words. Now, what is the proper capitalization?↵
</spoiler>↵
↵
↵
<spoiler summary="Step 4">↵
Take a look at: ↵
↵
```↵
use↵
the ↵
prufer ↵
code ↵
```↵
↵
Notice how the letters `UTPC` line up along the left. This indicates that we should only capitalize those letters, for the final answer of:↵
↵
```↵
Use ↵
The ↵
Prufer ↵
Code ↵
```↵
↵
If you used ü instead of u, that is also accepted.↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:13,a] Best Problem Ever ↵
- [likes:13,b] Best Problem Ever ↵
- [likes:13,c] Best Problem Ever ↵
- [likes:13,d] Best Problem Ever ↵
- [likes:13,e] Best Problem Ever↵
</spoiler>↵
↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
Just print the number of circles in the image. There are `7` if you include the circles in `i` and `?`.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:1,a] Best Problem Ever ↵
- [likes:1,b] Incredible Problem↵
- [likes:1,c] Amazing Problem↵
- [likes:1,d] Great Problem↵
- [likes:1,e] Good Problem↵
</spoiler>↵
↵
[B — Right or Wrong?](https://codeforces.me/gym/106452/problem/B) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Solution">↵
The title implies that you should check if the 3 numbers are "right" or not. You can do this by checking that $a$, $b$, and $c$ form the side lengths of a right triangle, with $c$ as the hypotenuse.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:2,a] Best Problem Ever ↵
- [likes:2,b] Incredible Problem↵
- [likes:2,c] Amazing Problem↵
- [likes:2,d] Great Problem↵
- [likes:2,e] Good Problem↵
</spoiler>↵
↵
[C — New Sorting Algorithm](https://codeforces.me/gym/106452/problem/C) ↵
Author: [user:ChiMasterBing,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
You are sorting a permutation, so all you have to do is print out the integers from $1$ to $n$, inclusive. The time constraints are very lax for this. Though you should be careful of the memory limit. If you read the second line entirely, you will probably get MLE. If you form a large string and then print it out, you will probably get MLE.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:3,a] Best Problem Ever ↵
- [likes:3,b] Incredible Problem↵
- [likes:3,c] Amazing Problem↵
- [likes:3,d] Great Problem↵
- [likes:3,e] Good Problem↵
</spoiler>↵
↵
[D — Subset Sums](https://codeforces.me/gym/106452/problem/D) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
<spoiler summary="Hint 1">↵
Clearly, solving this problem as is is too hard. Is there anything that you are missing here?↵
</spoiler>↵
↵
↵
<spoiler summary="Hint 2">↵
Try pressing Ctrl+A to highlight all the text.↵
</spoiler>↵
↵
↵
<spoiler summary="Solution">↵
If you highlight the space below "Notes," you will see the following equations:↵
↵
↵
If you plot these functions in Desmos, you will realize that $a$ is still a variable. By setting $a$ to $0$, $1$, and $2$, you will see the equations spell out `XOR`.↵
↵
This signifies that the question is actually asking about how many subset XOR sums equal $k$. This can be done in $O(n\log \max{a_i})$↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:4,a] Best Problem Ever ↵
- [likes:4,b] Incredible Problem↵
- [likes:4,c] Amazing Problem↵
- [likes:4,d] Great Problem↵
- [likes:4,e] Good Problem↵
</spoiler>↵
↵
[E — Gemini](https://codeforces.me/gym/106452/problem/E) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
Castor and Pollux are the twin stars of the Gemini constellation, but it seems like we can only see Castor...↵
↵
<spoiler summary="Step 1">↵
To solve Castor's problem, all even numbers must be put into separate sets. It can be shown that the required number of sets is always equal to $\lfloor\frac{n}{2}\rfloor$. You can do this by pairing `1 2`, `3 4`, `5 6`, etc. for even values of $n$. If $n$ is odd, you can instead do `n-2 n-1 n` for the last set.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 1.5">↵
After submitting, you will receive a verdict of `Хороший! Now help solve Pollux's problem!` This signifies that you should now look at Castor's partner, Pollux, since he also has a problem to solve. This can be done by switching your language to Russian.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 2">↵
To solve Pollux's problem, just write any sieve to print out the primes up to $n$.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 2.5">↵
At this point, you will probably get a verdict of `Oops, now Castor is getting a Wrong Answer on his end.` This means you should somehow solve both of their problems at the same time. (This is where the weird output format comes into play)↵
</spoiler>↵
↵
↵
<spoiler summary="Step 3">↵
To solve both of their problems, first print out all of the primes in one set to satisfy Pollux's problem. Then, try to complete the original construction from Castor's problem, but skip over any instance where you have already placed a number into the set of primes. Also, place $1$ into any set other than the first set.↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:5,a] Best Problem Ever ↵
- [likes:5,b] Incredible Problem↵
- [likes:5,c] Amazing Problem↵
- [likes:5,d] Great Problem↵
- [likes:5,e] Good Problem↵
</spoiler>↵
↵
[F — Something's Fishy](https://codeforces.me/gym/106452/problem/F) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02] ↵
↵
This problem has the exact same name as [a previous UTPC April Fools problem](https://codeforces.me/gym/105071/problem/E), and it also has some cursed numbers in it, though this time it relates to a different fish.↵
↵
<spoiler summary="Solution">↵
↵
<spoiler summary="Step 1">↵
First, we should solve for the variables. ↵
$X = 2206$ ↵
$a = 14$, this should include the one that just happened before this contest ↵
$r = 3$, no the answer is not $2$, are you an AI model? ↵
$c = 37$, a reference to [this video](https://www.youtube.com/watch?v=d6iQrh2TK98) ↵
$l = 1$, this is [Legendre's Constant](https://en.wikipedia.org/wiki/Legendre%27s_constant) ↵
$j = 31$, July always has $31$ days ↵
$h = 11$, there are $9$ [Heegner numbers](https://en.wikipedia.org/wiki/Heegner_number), and $11$ is the median of all of them ↵
$m = 777$, [Matikanefukukitaru](https://gametora.com/umamusume/characters/105601-matikanefukukitaru) has a skill that activates with $777$m left in the race, she is also closely related to luck in general (and so is $777$)↵
↵
Note that the $|$ operator denotes concatenation.↵
↵
So, $Y = 143\cdot (37+10)\cdot 131\cdot 11777 \mod 10^9+7$, which gives us $Y=369071357$.↵
↵
Now, what can we do with $2206$ and $369071357$?↵
</spoiler>↵
↵
<spoiler summary="Step 1.5">↵
If you pay attention to the flavor text, it mentions something about the ICPC Championship in Asia, which is on Codeforces, and is quite recent. If you click into the contest and look at the URL, the ID of the contest is also $2206$, so what about $369071357$?↵
</spoiler>↵
↵
<spoiler summary="Step 2">↵
If you look at submission $369071357$ from the 2026 Asia Pacific Championship, you will get [this submission](https://codeforces.me/contest/2206/submission/369071357).↵
</spoiler>↵
↵
<spoiler summary="Step 3">↵
Looking at the code, it is a compile error, which is very suspicious, and there is a massive template, which is not immediately suspicious. That is, until you realize that some parts of the template are quite suspect, such as `#define N number`. When would that ever be useful? If you take all of the suspicious parts and read the capital letters in order, they will spell `ANSHIDDEN`, which should tell you that the answer is `HIDDEN`.↵
↵
<spoiler summary="Tip">↵
You can diff the submission against a previous submission to see what got changed.↵
</spoiler>↵
↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:6,a] Best Problem Ever ↵
- [likes:6,b] Incredible Problem↵
- [likes:6,c] Amazing Problem↵
- [likes:6,d] Great Problem↵
- [likes:6,e] Good Problem↵
</spoiler>↵
↵
[G — Forgot where I took this pic](https://codeforces.me/gym/106452/problem/G) ↵
Author: [user:zmonster8,2026-04-02] ↵
↵
<spoiler summary="Solution">↵
Play Geoguessr. Any coordinate within 110 meters will be accepted. The real location is at `22.2763644 114.1568149`. You can also try to triangulate the spot since the checker will tell you how far you are.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:7,a] Best Problem Ever ↵
- [likes:7,b] Incredible Problem↵
- [likes:7,c] Amazing Problem↵
- [likes:7,d] Great Problem↵
- [likes:7,e] Good Problem↵
</spoiler>↵
↵
[H — Fill in the Blanks](https://codeforces.me/gym/106452/problem/H) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Hint">↵
It seems like increasing the index decreases the value, and decreasing the index increases the value. Also, the first element is "bad" for some reason.↵
</spoiler>↵
↵
↵
<spoiler summary="Solution">↵
You should not interpret $a_i$ as the $i$th element of a list. Rather, you should think of $a_i$ as some value $a$ in base $i$. This matches the ideas from the previous hint, and base 1 is not well defined. So the problem is simply to convert $a$ from base $i$ to base $j$. The constraints imply that the true value of $a$ does not exceed $10^{18}$. $j$ is always at most $10$, so the answer will always be numeric.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:8,a] Best Problem Ever ↵
- [likes:8,b] Incredible Problem↵
- [likes:8,c] Amazing Problem↵
- [likes:8,d] Great Problem↵
- [likes:8,e] Good Problem↵
</spoiler>↵
↵
[I — Networking Problem](https://codeforces.me/gym/106452/problem/I) ↵
Author: [user:25huangvictoria,2026-04-02]↵
↵
<spoiler summary="Solution">↵
If you submit anything, you will get a verdict of `Connection request pending. Have you checked the 6th floor?` Checking the 6th floor of the GDC will lead you to a QR code that will link to a LinkedIn profile. Connecting will give back an automated response telling you that the answer is: `I have added Victoria Huang on LinkedIn!`. (Please don't spam)↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:9,a] Best Problem Ever ↵
- [likes:9,b] Incredible Problem↵
- [likes:9,c] Amazing Problem↵
- [likes:9,d] Great Problem↵
- [likes:9,e] Good Problem↵
</spoiler>↵
↵
[J — Guess the Number!](https://codeforces.me/gym/106452/problem/J) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Solution">↵
At first, this seems impossible, until you realize that you have $4!=24$ queries, not $4$. For $1\le x\le 10^6$, binary searching on the answer will need $20$ queries, so $24$ is more than enough.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:10,a] Best Problem Ever ↵
- [likes:10,b] Incredible Problem↵
- [likes:10,c] Amazing Problem↵
- [likes:10,d] Great Problem↵
- [likes:10,e] Good Problem↵
</spoiler>↵
↵
[K — Guessing Game](https://codeforces.me/gym/106452/problem/K) ↵
Author: [user:walrusramen21,2026-04-02]↵
↵
<spoiler summary="Solution">↵
↵
<spoiler summary="Step 1">↵
After looking at the clues, you should realize that the answers cannot really be words. Each clue should solve to a year instead, but years have $4$ digits, and this game of Wordle has $5$ blanks...↵
</spoiler>↵
↵
↵
<spoiler summary="Step 2">↵
The hint says that `The present is built upon the results of the past.` This implies that you should look at the "results of the past," specifically the [past Wordle answers.](https://www.fiveforks.com/wordle/)↵
↵
You should get: ↵
1. 1646 $\rightarrow$ QUILT ↵
2. 1612 $\rightarrow$ CLAMP ↵
3. 1578 $\rightarrow$ FORUM ↵
4. 1596 $\rightarrow$ MOTEL ↵
↵
So, the final answer should be `MAUVE`.↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:11,a] Best Problem Ever ↵
- [likes:11,b] Incredible Problem↵
- [likes:11,c] Amazing Problem↵
- [likes:11,d] Great Problem↵
- [likes:11,e] Good Problem↵
</spoiler>↵
↵
[L — MST](https://codeforces.me/gym/106452/problem/L) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
<spoiler summary="Solution">↵
This would require some code if this were an actual MST problem, but of course, it is not. Note that the question does not specify that the graph must be connected, so we can just choose to take none of the edges (also, all edges have positive weight). This means the answer is just always `0`.↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:12,a] Best Problem Ever ↵
- [likes:12,b] Incredible Problem↵
- [likes:12,c] Amazing Problem↵
- [likes:12,d] Great Problem↵
- [likes:12,e] Good Problem↵
</spoiler>↵
↵
[M — META](https://codeforces.me/gym/106452/problem/M) ↵
Author: [user:m7a1g5i8k8a1r4p0,2026-04-02]↵
↵
This metapuzzle is in the style of a [puzzlehunt](https://blog.vero.site/post/puzzlehunts).↵
↵
<spoiler summary="Clues by problem">↵
↵
<spoiler summary="A">↵
Alternative medicine focused on specific points on the body using one's hands (11)↵
</spoiler>↵
↵
↵
<spoiler summary="B">↵
Something you "pass in", or an altercation (8)↵
</spoiler>↵
↵
↵
<spoiler summary="C">↵
Something you can do with a car, or something you can "catch" (5)↵
</spoiler>↵
↵
↵
<spoiler summary="D">↵
Stereotypically found in cartoons when someone is running very fast (4 5)↵
</spoiler>↵
↵
↵
<spoiler summary="E">↵
Guard, or someone who refrains from disclosing the location of their favorite restaurant (10)↵
</spoiler>↵
↵
↵
<spoiler summary="F">↵
Certain type of lounge for smoking (6)↵
</spoiler>↵
↵
↵
<spoiler summary="G">↵
Symbol representing ejection in a match (3 4)↵
</spoiler>↵
↵
↵
<spoiler summary="H">↵
Type of competition used in the Olympics that allows for second chances (9)↵
</spoiler>↵
↵
↵
<spoiler summary="I">↵
Common type of appetizer for those who cannot choose just one item (7)↵
</spoiler>↵
↵
↵
<spoiler summary="J">↵
Common action in Minecraft, or a type of fish (5)↵
</spoiler>↵
↵
↵
<spoiler summary="K">↵
Something found in grandparents' homes, or something found behind certain windows (9)↵
</spoiler>↵
↵
↵
<spoiler summary="L">↵
Alice's location (10)↵
</spoiler>↵
↵
</spoiler>↵
↵
↵
<spoiler summary="Solution">↵
You should solve all of the clues first.↵
↵
<spoiler summary="Answers to clues">↵
The parentheses indicate the enumeration of the answer to a clue. So "fish" would be (4) and "magic carp" would be (5 4) ↵
Also, after solving some of the clues, you will probably realize that all of the answers are in alphabetical order.↵
↵
<spoiler summary="A">↵
`ACUPRESSURE`↵
</spoiler>↵
↵
↵
<spoiler summary="B">↵
`ARGUMENT`, you pass in arguments in code, and get into arguments as an altercation↵
</spoiler>↵
↵
↵
<spoiler summary="C">↵
`DRIFT`, you can drift in a car, and you can catch someone's drift↵
</spoiler>↵
↵
↵
<spoiler summary="D">↵
`DUST CLOUD`↵
</spoiler>↵
↵
↵
<spoiler summary="E">↵
`GATEKEEPER`, this is modern parlance↵
</spoiler>↵
↵
↵
<spoiler summary="F">↵
`HOOKAH`, search up "hookah lounge"↵
</spoiler>↵
↵
↵
<spoiler summary="G">↵
`RED CARD`↵
</spoiler>↵
↵
↵
<spoiler summary="H">↵
`REPECHAGE`, this is used primarily in [Olympics wrestling](https://www.olympics.com/en/news/what-is-repechage-rules)↵
</spoiler>↵
↵
↵
<spoiler summary="I">↵
`SAMPLER`↵
</spoiler>↵
↵
↵
<spoiler summary="J">↵
`SMELT`, furnaces smelt in Minecraft, smelt is also a fish: https://en.wikipedia.org/wiki/Smelt_(fish)↵
</spoiler>↵
↵
↵
<spoiler summary="K">↵
`WALLPAPER`, wallpaper is found in older homes, and it is also what is behind windows (or tabs) on a computer↵
</spoiler>↵
↵
↵
<spoiler summary="L">↵
`WONDERLAND`↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Step 0.5">↵
"Undirected acyclic connected graph" just means "tree," so this puzzle should be about trees somehow. There is also mention of "trim[ming]" the trees.↵
</spoiler>↵
↵
↵
<spoiler summary="Step 1">↵
If we "trim" some of the answers, we can see some trees show up, though they might be anagrammed. As an example, trimming WALLPAPER gives us LPAPE. Anagramming this gives us APPLE.↵
↵
<spoiler summary="Trees after trimming">↵
ACUPRESSURE $\rightarrow$ SPRUCE ↵
ARGUMENT $\rightarrow$ GUM ↵
DRIFT $\rightarrow$ FIR ↵
DUST CLOUD $\rightarrow$ LOCUST ↵
GATEKEEPER $\rightarrow$ TEAK ↵
HOOKAH $\rightarrow$ OAK ↵
RED CARD $\rightarrow$ CEDAR ↵
REPECHAGE $\rightarrow$ PEACH ↵
SAMPLER $\rightarrow$ MAPLE ↵
SMELT $\rightarrow$ ELM ↵
WALLPAPER $\rightarrow$ APPLE ↵
WONDERLAND $\rightarrow$ ALDER ↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Step 2">↵
Now that we have a list of trees, we should consider what the `1. [5] -> 8` stuff means. Usually, [5] indicates that we extract the 5th letter from some word/phrase. But the second row wants us to extract the 5th letter from GUM, which doesn't exist. So, let's sort the trees in alphabetical order, then perform the extraction.↵
↵
<spoiler summary="Extracted letters">↵
ALDER $\rightarrow$ R ↵
APPLE $\rightarrow$ E ↵
CEDAR $\rightarrow$ ED ↵
ELM $\rightarrow$ E ↵
FIR $\rightarrow$ FR ↵
GUM $\rightarrow$ U ↵
LOCUST $\rightarrow$ S ↵
MAPLE $\rightarrow$ PE ↵
OAK $\rightarrow$ O ↵
PEACH $\rightarrow$ H ↵
SPRUCE $\rightarrow$ UC ↵
TEAK $\rightarrow$ T ↵
</spoiler>↵
↵
</spoiler>↵
↵
↵
<spoiler summary="Step 3">↵
The letters we have so far don't make any sense, so let's use the information to the right of the arrows (the 8 from `1. [5] -> 8`). Looking at all of these numbers, we see that they form a permutation of the first 16 positive integers, so let's use those numbers as indices into a 16-letter phrase. Then, we can rearrange the letters we have so far to uncover `USETHEPRUFERCODE` ("use the prufer code", which [relates to trees](https://en.wikipedia.org/wiki/Pr%C3%BCfer_sequence)!). This matches up with the final answer being 4 words. Now, what is the proper capitalization?↵
</spoiler>↵
↵
↵
<spoiler summary="Step 4">↵
Take a look at: ↵
↵
```↵
use↵
the ↵
prufer ↵
code ↵
```↵
↵
Notice how the letters `UTPC` line up along the left. This indicates that we should only capitalize those letters, for the final answer of:↵
↵
```↵
Use ↵
The ↵
Prufer ↵
Code ↵
```↵
↵
If you used ü instead of u, that is also accepted.↵
</spoiler>↵
↵
</spoiler>↵
↵
<spoiler summary="Feedback">↵
- [likes:13,a] Best Problem Ever ↵
- [likes:13,b] Best Problem Ever ↵
- [likes:13,c] Best Problem Ever ↵
- [likes:13,d] Best Problem Ever ↵
- [likes:13,e] Best Problem Ever↵
</spoiler>↵
↵
