"Euler Seven Bridges?"

Ying Yingying's face was cute, "This...... I've only heard of it, but I don't know exactly what it is. ”

Just as Cheng Nuo was about to explain, Li Shiye, who had been sitting on the side without saying a word, said slowly.

"At the beginning of the 18th century in Königsberg, Prussia, there was a river running through it, with two small islands and seven bridges linking the two islands to the riverbank. One person asked the question: how can a walker walk through seven bridges at once without repeating or missing a beat, and finally return to the starting point. This is known as the Euler Seven Bridges problem. But the problem of the Euler Seven Bridges itself is unsolvable. ”

At that time, the famous mathematician Euler transformed Euler's seven-bridge problem into a new concept - a one-stroke drawing! ”

"One, all the points on the graph are even. ”

"Two, there are only two singularities in the graph, and all the remaining points are even. ”

"The same is true for converting a flat shape into a three-dimensional shape. Li Shiye raised his chin, pointed to the two people who were participating in the challenge on the screen, and said, "So, the two of them, they don't need to go through every shape and each point of the route in their minds. You only need to look at whether the points of an irregular three-dimensional polygon are even or singularities to determine whether you can draw in one stroke!"

Cheng Nuo next to him has a black line.

Sister, I'm forcing you to pretend to be gone, what else am I pretending?

"But......" Li Shiye's tone changed at the end, "even so, the difficulty of this project is still very high. Every point on the irregular three-dimensional polygon, the two of them need to confirm it all before they can make their own judgment. ”

"This challenge is not as complicated as it seems. But it's definitely not worth just 8 points!"

Obviously, Li Shiye's words were said to Cheng Nuo.

"But I just think this challenge project is very simple!" Cheng Nuo flattened his mouth, looking very aggrieved.

Li Shiye was also annoyed by Cheng Nuo, pointed to the screen in front of him and said, "Okay, since you think this project is simple, then please Cheng Nuo, you tell me, is the three-dimensional polygon that Sun Meng is observing now?"

On the screen, Sun Meng from Peking University was standing in front of a three-dimensional polygon, frowning and pondering.

Although it is only necessary to determine whether all the points on the three-dimensional polygon are even or only two singularities, it is also a lot of work for the ordinary human brain.

On a three-dimensional polygon, there are seventeen or eighteen points to say the least.

At each point, the player needs to observe the bit. See if the number of segments connected to this point is odd or even.

It's an odd number, and this point is the singularity. If it's an even number, it's an even point.

If you count down such a line segment, if you have a lot of three-dimensional polygons, the player needs to count more than 100 line segments, which is quite a large number!

The shape of the polygon in front of Sun Meng at this time was obviously a little more complex than the other observations.

Therefore, Sun Meng's observation took longer.

In the lounge, Cheng Nuo simply glanced at the screen, and the data about the irregular three-dimensional polygon that Sun Meng was observing appeared in Cheng Nuo's mind.

There are 26 points, 38 line segments, 24 even points, and 2 singularities.

Looking at the data, it meets the conditions of the second stroke. The number of singularities is 2.

So......

Cheng Nuo replied casually, "This polygon can be drawn in one stroke. ”

Li Shiye glanced at Cheng Nuo suspiciously, because the camera on the screen switched quickly, he didn't have time to verify Cheng Nuo's answer, and he didn't know whether what Cheng Nuo said was right or not.

"What about this one?" Li Shiye continued to ask.

The camera on the screen has switched to Zhang Zheng's side, and Zhang Zheng at this time is also frowning in front of an irregular three-dimensional polygon.

Cheng Nuo simply glanced at the screen again, and didn't seem to have much observation and calculation, and gave his answer in the next second, "This can't be painted." ”

Li Shiye glanced sideways at Cheng Nuo. Because the camera stopped on Zhang Zheng's body for a long time this time, it was enough for Li Shiye to judge whether the three-dimensional figure on the screen could be a single stroke.

Seven or eight seconds later, Li Shiye, who had already come up with an answer, turned his head to look at Cheng Nuo and exhaled lightly, "You're right." ”

Just now he observed a total of five points of this irregular three-dimensional polygon. Three were found to be singularities and two were even.

It has become clear that this three-dimensional polygon can not be drawn in one stroke!

What made Li Shiye wonder was that even it took seven or eight seconds for him to figure it out.

But why did Cheng Nuo give an instant answer just by looking at it?

This is not scientific!

On the screen, Zhang Zheng, a student from Tsinghua University, slowly shook his head and denied the answer after observing the irregular three-dimensional polygon in front of him for nearly twenty seconds.

At this point, the camera cuts to the sky and gives a panoramic view of the 200 irregular three-dimensional polygons.

A huge stream of data slowly emerged in Cheng Nuo's eyes, and then transmitted Cheng Nuo's brain.

No. 1 solid polygon, 21 points, 29 line segments, 6 singularities, 15 even points.

No. 2 solid polygon, 18 points, 25 line segments, 2 singularities, 16 even points.

............

No. 200 three-dimensional polygon, 26 points, 35 line segments, 4 singularities, and 24 even points.

The footage just gives two or three seconds of panorama time.

But two or three seconds is enough for Cheng Nuo.

Soon, the camera switched back to Sun Meng of Peking University.

Li Shiye, who was sitting on the side, wanted to speak and repeat the previous question, but was interrupted by Cheng Nuo in advance. "Li Shiye, I know what you want to ask me. ”

"In order not to trouble you to ask one by one, I will answer you all at once. ”

Cheng Nuo smiled faintly and said unhurriedly, "Of the 200 irregular three-dimensional polygons on the field, there are a total of 45 that meet the conditions for a single stroke. ”

"Well, the numbers are No. 2, No. 6, No. 11,...... Number 198!"

"How is it, classmate Li Shiye, are you satisfied with this answer?"

Cheng Nuo looked at Li Shiye and said with a smile.

"Are you ......" Li Shiye looked at Cheng Nuo in a daze, and was silent for a long time before he held back a sentence, "These...... You don't make it all up, do you?"

It's not that Li Shiye has to think like this, but Cheng Nuo's performance is really a bit too much.

That's 200 solid polygons!

Let it be him, observe it all, it is impossible to have more than ten or twenty minutes!

But how long did Cheng Nuo take? a few seconds!

How is it possible to look at all 200 figures in a few seconds?

Facing Li Shiye's questioning, Cheng Nuo just shrugged, "Whether what I said is right or not, you will know in a moment." ”

............

Every haircut is like gambling, and this time it'...... I lost my bet!

It's ugly~~~