87: Chapter 87 Ali Preliminary Round

At 8:00 AM on April 23rd, the preliminary round of the Alibaba Global Mathematics Competition officially opened.

This was not a traditional two-hour closed-book exam.

It lasted from 8:00 AM on the 23rd until 8:00 AM on the 26th.

Seventy-two hours.

It was more like an extreme test of mental endurance, information retrieval, logical reconstruction, and time management skills.

For many contestants, these seventy-two hours meant compressed sleep, increasingly messy draft papers, cold coffee, and problem statement files repeatedly opened and closed.

As well as repeatedly doubting whether their past accumulation was an illusion, and doubting whether they even knew math at all.

But for Jiang Lin, it felt more like a long-cycle system task.

It wasn't a competition of who sat in front of the screen longer, nor was it about who could keep their eyelids open to calculate calculus after pulling two all-nighters.

Instead, it was about who could stably read the problems, strip away the packaging, build mathematical models, deduce and verify, and finally organize impeccable expressions over three full days.

Most importantly, it was about not letting other real-world tasks come to a complete standstill during this process.

After the problem statements opened, the first step was to download them.

Save.

Create hierarchically structured folders on the local disk.

Ali_Prelim_2022/

├── problems/

├── scratch/

├── solutions/

├── submit/

└── submit_record/

Only then did he open the PDF file in problems and begin reading through it.

Eleven problems.

Glancing over them roughly, the problem statements exuded a deliberate sense of approachability.

The snowflake arrangement for the Winter Olympics opening ceremony, delivery route planning for courier stations, the assembly of magnetic geometric magic cubes played by children, and the blind box drawing games popular among young people.

Along with some seemingly everyday, gamified, and engineered narratives.

If they were green undergraduates, they might be fooled by such problem statements, thinking they could easily conquer them just by knowing a bit of simple combinatorial mathematics and probability theory.

But the more everyday the problem statement looked, the deeper the traps were usually buried, making it the easiest for people to misjudge and ultimately fail halfway through.

Because it wasn't testing whether you could recite a certain theorem.

Instead, it tested whether you could strip out the true mathematical structure from this warm, everyday packaging.

Jiang Lin divided his draft paper into three columns.

[Can write directly]

[Needs expression organization]

[Prone to misjudging problem intent]

After reading through the first time, he didn't label any problem as difficult or simple.

These two words were too crude and too subjective in a true mathematical context.

He only marked the risks.

For the magnetic geometric magic cube problem, the risk did not lie in spatial imagination, but in mistaking spatial imagination for proof.

If one relied solely on drawing diagrams and enumerating configurations, it was very easy to write down a large pile of beautiful but non-exhaustive assembly schemes.

The truly difficult part was that you had to prove the upper bound, proving that no missed extreme configuration could break through this upper bound.

As long as it couldn't be exhausted, it wasn't a mathematical proof, but at best an experimental observation report.

The risk of opening blind boxes did not lie in the expectation itself.

Markov chains and the linearity of expectation were foundational tools.

Its true trap lay in the state definition.

If the state space was chosen wrongly from the beginning, carrying one more seemingly harmless variable would cause the recurrence dimension to expand rapidly, making the final formula look complete yet very difficult to review, and making it hard to prove that one hadn't double-counted or missed boundaries.

...

After reading these problems carefully, Jiang Lin wrote down their numbers in the [Needs expression organization] column.

It wasn't that he couldn't do them.

His train of thought had already formed a closed loop in his mind by the second reading.

The problem was whether others could stably review and verify the answers once they were written out.

The official solutions of a math competition weren't scribbled notes meant only for oneself.

They had to cross the network and be handed to equally exhausted and picky grading professors on the other end.

To withstand grading, you had to ensure that the logical chain was a completely closed steel rail, rather than a pile of scattered iron sheets.

Furthermore, one must make every effort to avoid hiding crucial logical leaps behind vague phrases like obviously, easily obtainable, or not hard to prove.

On the morning of the 23rd, Jiang Lin finished three relatively straightforward problems.

In the afternoon, he went to Jiangda University to audit a special lecture on space Physics.

Returning at night, he continued organizing the submission versions for two of them.

On the 24th, he handled emails from the quantitative platform side, only replying to necessary content without starting new projects.

In the evening, he revised another problem.

Originally it could be finished on one page, but it eventually turned into two and a half pages.

Because the one-page version was too beautiful, using an extremely clever symmetry scaling, carrying even a trace of a flash of artistic inspiration.

But reading it felt like the answer had dropped straight from the sky.

Without footprints or provenance.

For the graders, if they couldn't catch up with this flash of inspiration at the first moment, they would suspect whether there were undiscovered counterexamples in the scaling process.

Meanwhile, the two-and-a-half-page version looked a bit bloated and somewhat clumsy, but every step had a solid landing point.

One only needed to follow the logic downwards to reach the finish line without any suspense.

On the evening of the 25th, Jiang Lin finished organizing all eleven problems.

Waiting until six o'clock in the early morning of the 26th.

Washing up, drinking water.

Opening the computer.

Rereading starting from the first problem.

Checking three things for every problem.

First, whether the problem intent was misread.

Second, whether boundaries were missed.

Third, whether unproven intuition was written down as a conclusion.

Forty-five minutes later, the review ended.

No fractures at the self-verification level were found, and only two subscript spelling errors were corrected.

At 7:38, he clicked on the submission page and submitted.

The page prompted that the upload was successful.

He habitually pressed the screenshot shortcut key and saved it.

At exactly 8:00, as the time in the bottom right corner of the computer ticked, the webpage automatically refreshed, prompting that the competition had ended.

The problems changed from competition materials to discussion materials.

Jiang Lin closed the page, leaned back in his chair, and did not celebrate with a long sigh of relief.

For him, the Alibaba preliminary was a coin, a new real-world credential.

The problems had been submitted, and the answers had left his scope of control.

What could determine the result next wasn't him refreshing the screen a few more times, but the judgment of the graders on the other end.

Competition results could become a stepping stone, but they could not become a reason for him to stop.

There was a document to be picked up at Jiangda University in the afternoon.

Last week, he made a list and asked Senior Brother Meng Che to help download a few raw data descriptions of MMS satellite magnetospheric reconnection events, instrument calibration documents, and a few controversial event analysis papers from recent years from the school database.

At 3:10 PM, Jiang Lin rode his bicycle to Jiangcheng University.

Familiar Physics Building B, Room 304.

Three familiar people.

Meng Che sat by the window with his legs crossed, drinking coffee while snatching a moment of leisure.

He hadn't participated in this competition.

Towards the commotion of the Alibaba preliminary, he only maintained an interest of watching the excitement without being completely a layman.

Yin Hang stood in front of the whiteboard, holding a marker with a tightly knitted brow.

Three printed problem statements had already been magnetized to the whiteboard, next to which were filled with various geometric shapes, arrows, and scribbled formulas.

Yao Siyu sat by the long table in the middle, with a thick stack of draft paper spread out in front of her, on which several long probabilistic recurrence formulas were written.

Two of the sections were heavily crossed out with a red pen, next to which a clear annotation was marked.

Hearing the door click, the three of them raised their heads simultaneously.

Meng Che's gaze shifted away from the screen, and seeing it was Jiang Lin, he smiled and spoke first.

"Has the seventy-two-hour penal servitude ended?"

"It has ended."

Yin Hang turned around, the marker in his hand spinning skillfully between his fingers.

He was a straightforward person with an aggressive streak in doing academic work, and his first sentence went straight to the point: "What time did you submit?"

"Seven-thirty-six."

Yao Siyu pushed up her glasses, her gaze lingering on Jiang Lin's face, trying to find a trace of breakdown from staying up late, but found nothing.

"How many did you write?"

"I wrote all of them."

The room suddenly fell silent for a second.

This sentence definitely didn't mean all eleven were correct.

In a math competition, no one dared to claim they got everything right before the results came out.

But for a test paper of the intensity of the Alibaba preliminary, the mere fact that all eleven problems were written already represented a terrifying level of stress resistance and execution capability.

By the third day, many people didn't even have the courage to take a glance at the remaining problems.

"Did you write general approaches, or did you make full submissions?" Yin Hang asked.

"Full submission."

"Eleven complete drafts, not drafts, the kind of complete with boundaries and exceptional cases?"

"Yes."

Looking thoughtful, Yao Siyu pushed a problem statement to the middle of the table.

"It's good that you're done. Help me take a look at this."