I am on the train, so I decided not to write any code (can’t be bothered to anyway ^_^) and instead rely on a coding assistant (claude code with kimi2.7) to implement everything based on my notes and directions. That way I’ll have something to submit and know if my idea was actually correct.

It is my first time doing coding problems in about a year, and this was more of an experiment for fun than a serious competition, but I still want to solve all the problems and get a perfect score :O.

The Process

For each problem, I followed roughly the same workflow:

  1. Read the problem statement. If it was poorly written or buried the actual task under a wall of story, I would use the bot to create my own simplified restatement first.
  2. Think about the solution. This is the main part I enjoy. After I have the solution, clean up my thoughts into a basic solution overview, anywhere from 2 to 50 bullet points. Then use these notes to generate a detailed solution explanation and implementation plan.
  3. Review the plan. Read through what it produced, catch anything wrong or unclear, and fill in important details I had glossed over in my own notes. Implementation tips went here too, along with a list of code templates I want to use.
  4. Let it implement. The bot would write the code, generate test cases, and produce a brute force solution for verification.
  5. Debug as needed. When there is a bug and the bot can’t fix it, guide it by deciding which intermediate variables to print, or isolating and testing just a part of the code.
  6. Verify and iterate. Generate different test types, measure performance, or walk through small examples by hand.

The process kind of reminded me of this one time when I was at ICPC and no one on my team had much experience, so I came up with the solutions while the others implemented everything. It actually worked very well and we completed all the problems that round lol. The problems here are much harder, but the bot is quite good at understanding my notes and knows all the common data structures.

Problem Review

The full solutions, generators, and test cases are available here, and each problem below links to its solution plan used to generate the code.

A

Solution outline →

I read through this one quickly and completely missed that hiding on an edge was possible until the samples didn’t match my node-only solution. The fix was straightforward once I noticed though.

Implementation elegance: 7/10 — Clean enough for a first problem.

Idea: 6/10 — Mostly straightforward, with just a small amount of original thinking required.

Quality of life: no complaints. Output as a fraction was a reasonable design choice.

B

Solution outline →

Decent problem

Implementation elegance: 8/10 — One of the cleaner solutions of the set.

Idea: 8/10

Quality of life: no complaints. (◕‿◕)

C

Solution outline →

I can see what the problem setter was going for, but the problem ended up feeling flat and uninspired. The underlying idea was not enough for an entire problem, so it ended up being combined with other well-known tricks while driving up the implementation complexity. This is something I run into often when setting my own problems: I have a concept I find interesting, but I struggle to translate it into a challenging or engaging task.

Implementation elegance: 4/10 — Although the idea was complex, my solution wasn’t as difficult to implement as I expected, with just some frequency hashmaps at its core. But then, in order to meet the time and memory constraints, I had to add coordinate compression and conversions between array, hashmap, and key-value pair lists which was annoying.

Idea: 5/10 — The concept was there, but it didn’t land well.

Quality of life: I appreciated the T=0 case, which saved me from dealing with query encryption during debugging. More samples would have helped. The problem statement was understandable and not too long.

One interesting note: using a tree instead of a list for this problem was necessary to prevent alternative solutions from slipping through. The time limit had to be tight to block O(n^1.5 log n) and O(n q) solutions from passing. But even so, those might still pass—which circles back to what I said earlier. When the problem gets too complicated, you end up with high constant factor and endlessly tuning constraints with time limit set to max 😩.

D

Solution outline →

The mirroring strategy was easy to guess but annoying to prove. After that, it just a lot of casework. From later testing, the bot was actually able to solve this problem and P1 independently, which was great for me (^_^)b.

Implementation elegance: 4/10 — Lots of annoying edge cases.

Idea: 3/10

Quality of life: The problem statement was hard to understand. I had to read it several times before it made sense.

E

Solution outline →

Implementation elegance: 5/10 — Lots of little things to calculate in multiple passes.

Idea: 7/10 — The underlying idea was solid.

Quality of life: Fine overall. I’d move the definition of a tree and the distance between two nodes to the end of the statement to separate important problem info from what most people already know.

Also, this was the third problem statement in this contest that describes one problem before adjusting it at the end for being “too easy”.

F

Solution outline →

I came up with the right approach quickly, but I made the mistake of trying to process the problem in increasing order instead of decreasing order. That led to an (incorrect) O(n^8) solution. Since it seemed to barely fit the time limit, I didn’t realize how much simpler the correct solution was for a long time.

Implementation elegance: 5/10 — Much less messy with the correct order, but there were still over 10 transition cases to work out by hand (the bot could do this for me once I told it to make a table with intermediate logical steps).

Idea: 7/10

Quality of life: The problem statement was a bit confusing because it used colors for both nodes and edges simultaneously. More samples would have helped for testing.

Overall Thoughts

There were some interesting problems in this contest. Even the boring ones weren’t too bad—though that may be because I didn’t have to implement and debug by hand.

I enjoyed coming up with ideas while the bot handled the parts I can’t be bothered with.

I probably won’t do a live contest anytime soon. I like solving problems, but implementing, debugging, and competing in contests causes me stress. Back when I was training daily, I enjoyed the shared excitement and discussing and comparing our solutions after the contest.

But since then, I’ve reached a level I’m satisfied with and stopped solving problems regularly. My friends in the competitive programming community have either lost touch or retired from the scene. And I have new work and activities that make blocking out three uninterrupted hours increasingly hard to justify.

That said, it could still be fun to solve a problem occasionally while waiting in line or in the bathroom. I haven’t been able to fully solve an IOI contest yet, so maybe I will do this year’s problems when they come out.