Chapter 147

"Euler seven bridge?"

Ying Ying Ying's face was cute, "this I've only heard of it, but it's not clear what it is. "

When Cheng Nuo is ready to explain, Li shiye, who has been sitting on one side, says slowly.

"At the beginning of the 18th century, there was a river running through gonesburg in Prussia. There were two small islands on the river. There were seven bridges connecting the two islands with the river bank. A man asked a question: how can a pedestrian walk seven bridges at a time without repetition and omission, and finally return to the starting point. This is the famous Euler seven bridge problem. But there is no solution to the problem of Euler seven bridge itself. "

"Euler, the famous mathematician at that time, transformed the problem of Euler's seven bridges and formed a new concept - a stroke! In addition, two sufficient conditions for one stroke figure are proposed

"One is that all the points on the graph are even points."

"Second, the graph has only two singular points, and all the remaining points are even points."

"It's the same thing when you convert plane graphics to solid graphics." Li shiye raised his chin, pointed to the two people who were taking part in the challenge on the screen and said, "so the two of them don't have to go through every figure and every point in their mind. We just need to observe whether the point of irregular solid polygon is even point or odd point to judge whether it can be stroke or not

There's a black line on the side of Cheng Nuo.

Younger sister, force all let you pretend to have no, what do I still pretend?

"But..." Li shiye finally changed his tone, "even so, the difficulty of this project is still very high. Each point on the irregular solid polygon needs to be confirmed by both of them before they can make their own judgment

"This challenge project is not as complicated as it seems. But it's not only 8 points! "

Obviously, this sentence of Li shiye is to Cheng Nuo.

"But I just think this challenge project is very simple." Cheng Nuo flat mouth, a pair of I am very aggrieved look.

Li shiye was also elated by Cheng Nuo. He pointed to the screen in front of him and said, "well, since you think this project is simple, please tell me something about it. Is this three-dimensional polygon that sun Meng is observing now, is it a one stroke three-dimensional polygon?"

On the screen, sun Meng, from Peking University, is standing in front of a three-dimensional polygon, frowning and meditating.

Although we only need to judge whether all the points on the solid polygon are even points or only two singular points, it is also a lot of work for the brain of ordinary people.

There are at least seventeen or eighteen points on a solid polygon.

At each point, the players need to observe in place. Let's see if the number of lines connected to this point is odd or even.

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

Such a number of line segments down, more words, a three-dimensional polygon, players need to count more than 100 lines, a considerable number!

The shape of the polygon in front of sun Meng is obviously a little more complicated than those observed by others.

Therefore, sun Meng's observation took longer.

On this side of the lounge, Cheng Nuo simply glanced at the screen, and the data about the irregular three-dimensional polygon sun Meng was observing appeared in Cheng Nuo's mind.

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

Look at the data, it meets the second stroke condition. The number of singularities is 2.

So

Cheng Nuo casually replied, "this polygon can be drawn with one stroke."

Li shiye looks at Cheng Nuo suspiciously. Due to the fast switching of the camera on the screen, he has no time to verify Cheng Nuo's answer and does not know whether Cheng Nuo is right or not.

"And this one?" Li shiye continued to ask.

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

Cheng Nuo is a simple glance at the screen, seems to have no observation calculation, the next second to give their own answer, "this can't be a stroke."

Li shiye glanced at Cheng Nuo. Because the camera stayed on Zhang Zheng for a long time, it was enough for Li to judge whether the three-dimensional figure on the screen could be stroke by stroke.

Seven or eight seconds later, the answer has been reached. Li shiye turns his head and looks at Cheng Nuo and breathes softly, "you're right."

Just now he observed five points of this irregular solid polygon. It is found that three are singular points and two are even points.

As a result, it is obvious that this three-dimensional polygon can not be stroke by stroke!

To Li shiye's surprise, it took seven or eight seconds for him to judge.

But why Cheng Nuo, just a glance, can give the answer in an instant?

It's not scientific!

On the screen, Zhang Zheng, from Tsinghua University, slowly shook his head and denied the answer after observing the irregular three-dimensional polygon in front of him for nearly 20 seconds.At this time, the camera cuts to the sky, giving the 200 irregular three-dimensional polygon a panoramic view.

A huge stream of data, slowly emerging in Cheng Nuo's eyes, is then transmitted to the brain.

There are 21 points, 29 lines, 6 odd points and 15 even points.

There are 18 points, 25 lines, 2 odd points and 16 even points.

…………

There are 26 points, 35 lines, 4 singular points and 24 even points.

The camera just gives two or three seconds of panoramic time.

But two or three seconds is enough for Cheng Nuo.

Soon, the camera again switched to sun Meng of Peking University.

Li Nuo, who wants to sit on the other side of the table, is interrupted by the question. "Classmate Li shiye, I know what you want to ask me."

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

Cheng Nuo light smile, not slow to open the mouth said, "the field of these 200 irregular three-dimensional polygon, a total of 45 in line with the conditions of a stroke."

"No. 2, No. 6, No. 11 198! "

"Well, Li shiye, are you satisfied with this answer?"

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

"You..." Li shiye stares at Cheng Nuo. After a long silence, he says, "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 too much.

That's 200 solid polygons!

It's him who will observe all of them. It's impossible without ten or twenty minutes!

How long did Cheng Nuo use it? A few seconds!

How is it possible to observe all 200 figures on one side in a few seconds?

In the face of Li shiye's query, Cheng Nuo just shrugged, "what I said is right or not, you will know in a moment."

…………

Every haircut is like gambling, this time I lost the bet!

It's ugly ~ ~ ~

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