The 2024 CCPC Jinan Contest ended on Oct 27. While this report was initially a requirement by our team coach, I think it may be valuable to repost it to Codeforces in English.
Preparation
The week before contest contained 2 team training sessions: 2022 China Collegiate Programming Contest (CCPC) Guilin Site and The 2021 CCPC Guilin Onsite (XXII Open Cup, Grand Prix of EDG), and we got 1 problem above the gold medal line in both, which enhanced our confidence. Our three teams, along with our coach (part of the contest committee), reached Jinan via high-speed railway a day prior to team registration.
During the dress rehearsal, a flaw on the contest floor(literal) immediately drew our attention: there was a narrow drain hole beneath one of my teammates' chair and a chair leg might get caught up causing him to fall over, and later we found we are not alone. We called staff over and they fixed it with cardboard taped to the ground. But the bigger problem is the keyboard: the \ and Enter almost switched place(compared to usual keyboard layouts), so when typing \n an actual carriage return plus an n will appear instead! To make things worse, it takes a smash to press down the right SHIFT and Backspace. The committee promised to replace keyboards in following contests.
Problems in the rehearsal were simple and one of them was from one of the two trainings above. We AKed (i.e. solved all) the 5 problems within 1h, and spent the remaining hour measuring the judgement server. At the preparation meeting that evening, teams shared their testing results including the speeds of:
*and/on double-precision FPs%operation on 64-bit integers__gcd()- Insertion and queries on
setmappriority_queue coutwith and without stream desyncing- NTT
The meeting was truncated because several contestants (including I) registered rated for ABC377 for a final warm-up.
Contest Day
I had a bad night's sleep, as air in Jinan is much drier than in Shanghai and the ventilation was not quite good. Luckily, it didn't affect much of my early-game performance.
Early Game
[0:00] We split the problemset by modulo 3 and Icedpiggy found the "Registration problem" A immediately.
[0:08] AC on A. I made marks on seemingly viable problems like B, C, I, L and M(which proved to be a trap eventually). Several green lights for J showed up on the scoreboard and Icedpiggy went to work. In the meantime, A-Quark found an $$$O(1)$$$ solution for B and explained it for me and I spent time confirming.
[0:32] AC on J. I coded B while A-Quark and Icedpiggy found the critical idea for problem I and later the correct approach for F.
[0:57] AC on B. Now Icedpiggy has 2 problems in his hand and coded them sequentially. The scoreboard was a bit messy now: we didn't know which should be the 6th problem and left observations on the printed problemset.
[1:20] AC on F. A-Quark and I started to form an idea for problem E, which was almost pure implementation and included big integer operations(which hampers C++). I am the only Python user in our team so it's up to me.
Midgame
[1:44] AC on I. I began to code E but I struggled with Python's input scheme and eventually gave up using map and wrote 6 separate int(str)s instead.
[2:08] Coding on E ended but the result of sample tests were ridiculous. A-Quark formed an idea for problem H (DP by digit) and fed it to Icedpiggy.
[2:31] WA on E. Icedpiggy coded his first draft of H but couldn't pass samples. Meanwhile A-Quark pointed out a crucial missing case in E.
[3:10] WA on E. We switched places and debugging for H continued. I asked A-Quark to leave observations on C(construction) and went on digging my head for the bug.
At this moment, I felt something was wrong: each of us is working on a separate problem.
[3:27] I found that I applied missing crucial case to only one of the major cases: it should apply to all. Icedpiggy kept failing samples on H and considered refactoring.
[3:39] WA on E for the 3rd time. I determined that it would be pointless to manually debug and quickly wrote a brute force and a data generator. The first round of STing produced exactly one error and I printed the test case. Icedpiggy completed refactoring under the assistance of A-Quark.
Last Moments
[4:00] Scoreboard frozen. I located the bug and fixed it immediately.
[4:07] RE on E. A second round of ST showed that the culprit was a useless floating point division that existed since the initial draft!
[4:19] AC on E finally! But I don't think 6 problems can earn us gold, and commanded A-Quark to continue assisting Icedpiggy and turned to C alone.
[4:40] I found the key construction structure for problem C but was still a step away from full solution. Problem H seems far from getting back onto the right track.
[4:50] I had the complete solution for C and preempted the keyboard for a final desperate sprint.
[4:59] WA on C.
