2025 ICPC Nanjing Travelogue
Day -1
I don’t know why, but recently I’ve been exceptionally fond of Jay Chou’s early songs, specifically the albums from before 2005, even though I previously leaned more towards his songs from 2006 to 2010. They are about the same age as I am. I feel that these ancient songs hold a faint yet mellow sadness, whereas the new songs from recent years seem somewhat flashy and frivolous. Among the old songs, “Sunny Day” is the most classic; for the first few years after I first discovered him in middle school, I didn’t think it was amazing, but now I have become the person described in the song.
My body felt terrible all morning, an indescribable discomfort, probably because the vp last night was too tiring. However, I currently plan to do CF tonight.
Day 0
November 7th, 2 AM, Hangzhou, Clear. My heart is so calm.
As long as there is a rating change of >=+40, I’m quite happy, and I achieved this goal tonight. Although E was nowhere near as difficult as I thought; dXqwq even wrote it in five minutes. It seems it was just running a Disjoint Set Union based on degrees and then calculating it. It turned out to be neither a Kruskal reconstruction tree nor an Euler path… I even thought about Prim.
I consider myself to have realized once again that there are difficult things in this world: upside-down dreams. 99% of things are difficult things; 99% of ideas lack the tools to be realized; 99% of approaches cannot ensure correctness.
Only that tiny fraction of things can be achieved. What we can do, and what we need to do, is absolutely not to achieve the impossible, but merely to find the things that can be done. Once found, they are naturally achieved. Or rather, what we need is to realize that we are attempting to achieve the impossible, and immediately abandon that attempt—sometimes, it means stopping this self-deception.
This requires a rapid and constant self-subversion in thinking.
Anyway, the late-night snack was delicious.
Where there is a will, there is a way. This statement is entirely wrong; only things that conform to scientific laws can be achieved. Most things people want to do, no matter how hard they try, cannot be achieved. We must eliminate the ninety-nine things out of a hundred that cannot be achieved and find the one that can. This is very hard, but we must do it!
—— Supernova Era
It is night now. Just took a shower. For some reason, I feel very excited. At least more excited than both contests last year.
Day 1
Coach Han entrusted us with a lot last night. I transcribed the coach’s words the night before, printed a copy of “Notes and Methodology,” and brought it to the exam venue on both days. It should be on our seats in the training team classroom now.
Woke up past seven in the morning. Went downstairs to split the luggage with a few teammates and then took a taxi to the East Station. After arriving at noon, we found the hotel was right near the subway station, very close. There was a strange smell in the room, but it was okay; after all, it was a single room for each person, which is much better than the dormitory environment…
Checked in, collected supplies, took group photos. Personally, I think the clothes for the Nanjing station look very good. Pity we went too late and the prizes for answering questions were gone.
Speaking of which, I still haven’t seen Gege [Brother], sigh.
When the warm-up match started, lyc pressed F4 and the computer went into tty mode, but it was restored after a restart with the help of a volunteer.
This day was lyc’s birthday! I ate ground pot chicken with fpy and his old friends, and we also had cake~ It felt very delicious~ And it was my first time eating it, the portion was huge too~
Wuwuwu, celebrating a birthday with friends is just too wonderful! At this moment, I secretly made up my mind that I must invite her to attend my birthday next week.
Day 2
Seem to have departed from the hotel past eight o’clock.
F
The first thing I looked at when the opening started was F. The problem statement was very short. After reading it, I immediately realized that this was definitely a solvable problem, and very likely to be solved early on. But at this moment, I began to suffer because I didn’t have any immediate ideas, especially since this involved dynamic graphs, online queries, connectivity, and the like. I feel I have almost never solved a simple one of these. It also involved bitwise operations. So I began to pray that I had underestimated the difficulty of this problem.
But the most painful thing was that jiangly solved this problem in the 8th minute!
Thus, this problem was displayed as a simple problem on the scoreboard. Since it is a simple problem, and jiangly wrote it in such a short time, how could it be building 4096 disjoint sets…? So thereafter, I kept hovering between two lines of thought: “There must be a simpler approach!” and “Maybe this problem is actually quite complex?”, spinning around endlessly.
First, I tried an approach of building 12 disjoint sets by bit, but it was completely unable to handle the case of multiple edges, because multiple edges would lead to the revocation of connectivity for lower-layer nodes. At that time, fpy advised me that a revocable Disjoint Set Union is at least a black-level problem, highly unlikely, and indeed that was the case. This approach seemed to be ; the complexity was satisfied, but the correctness could not be satisfied. After submitting, the time had reached 3:09:01.
Then I tried a subset enumeration approach. For a certain edge weight of a newly added edge, enumerate all its subsets, then connect the disjoint sets under the corresponding subsets, and query all of them. Correctness could definitely be guaranteed, but complexity could not be guaranteed; it was . Time reached 4:29:53.
Then Problem F collapsed. Affected by Problem F, I barely looked at other problems throughout the whole process.
After the scoreboard was frozen, I tried an approach that only enumerates the different binary suffixes for a certain newly added edge weight. I remember at first it couldn’t even pass the sample, then I added something and it passed the sample, can’t remember what. Time reached 4:55:00.
K
Then let’s talk about K, the chess problem, asking if there exists a strategy where the Rook can definitely catch the Knight. I can only say it’s a “one-glance” problem. If the Knight cannot escape after making one move, then it can definitely be caught. Just enumerate the eight directions and check.
I remember lyc seemed to be looking at this problem from the start, but he kept being unsure if the conclusion above was correct? After I finished writing C and guaranteed the correctness of the conclusion to him, he probably went to write it, but he wrote a dfs that returns when dep==2, which is acceptable but a bit hard to take. Since it was a sign-in problem, he seemed to debug it for quite a while. So after sorting out the implementation details, I kicked him off and went to write it myself. Felt it was quite fast, finished in a dozen lines, though I also debugged for a bit. Time reached 00:59:44.
fpy seemed to be looking at the kangaroo problem at the front initially, but he also quickly switched to F later, and was trying hard to communicate the approach for F with me the whole time, but I was a bit anxious then, head empty, head full, couldn’t listen.
Problem C was also handed to me by fpy. He said it was obvious at the time. I took a look, indeed, even numbers can definitely be split into two halves, odd numbers cannot equal an even number multiplied by an odd number, and it was done.
G
Of course, in the end, I was redeemed by lyc. Thanks LYC! He solved Problem G at 3:48:02, avoiding the bad luck of hitting iron. Actually, at this point, even if F was solved, we couldn’t get Silver anymore. This was only discovered after it ended.
He said Problem G was very simple. Seemed to have WA’d once at the start due to some range issue, didn’t understand, my state was not very good throughout.
After solving Problem G, lyc also gave me an approach for Problem I. The problem seemed to be finding ppap. He said it was enumerating two boundaries, using KMP to calculate boundaries, and then enumerating the inside once more, just counting. Because I usually write relatively fast, he tried to explain it to me a few more times for me to write, though in the end, I didn’t quite understand. He later also realized the first part seemed to be and couldn’t be done.
After the event, lyc told me that Problem I might have had more hope than Problem F. Problem F was just too much of a pitfall.
After it ended, I rushed to Nanjing South Station with the little kangaroo in my pocket, didn’t collect the award.
After
Depressed? Depressed, very depressed, tightly depressed, but there is also a feeling of relief. Maybe I won’t place so much importance on rating when playing cf in the future.
Retiring? It seems four people asked me if I was going to retire. How should I put it? I don’t know. Even though it is already the 18th now, I don’t know. Feel like it’s damn likely I’ll be persuaded to quit by the coach, what to do.
Speaking of being persuaded to quit, when chatting with fpy on the road afterwards, he said hyl was persuaded to quit by the coach back then because she was stuck at Green for two years. What kind of grapevine news is this. I always thought she quit on her own because she didn’t perform well in the HDU Spring contest. Sigh, after all, her performance in the 2024 Freshman Contest was really eye-catching.
However, I still believe hyl did something wrong. Because at that time her interests were closely related to mine, and due to other factors, I have too many, too many reasons not to forgive her.
Speaking of which, there is a relatively high possibility that lyc will quit; personally, I speculate fpy probably won’t.
Speaking of which, I don’t want to upsolve the problems from this contest, a bit of PTSD one might say. Of course, there will be opportunities to upsolve later.
The competition result really conforms to scientific laws, doesn’t it? In the few weeks before the contest, I vp’d at least five CCPC and ICPC contests. Except for getting Silver at the Hong Kong station, all were Bronze, without exception. Doesn’t this explain the problem very well? Performing extraordinarily well would be the violation of science.
(Off-topic, that RainbowChicken near Cuipingshan Subway Station and Wisteria Garden Hotel is really delicious! The portion is huge! And it’s cheap! Will order again next time if there’s a chance! Really delicious!)
Day 4
Luck was not bad. Played codeforces and solved a relatively simple D1. It was a mex problem that I like. Successfully ascended to Purple, 1959, fulfilling a cherished desire of over 500 days! Actually, during the cf on Day-1, I had a strong premonition that I would soon ascend to Purple, as if this premonition was forcefully pushing me up the ranks, allowing no refusal. But why didn’t this premonition assist me in performing well in the regional contest?
I feel it was precisely this somewhat “let it rot” mindset after failing to keep Silver that made me perform better.
2025/11/18 19:35:13