JD.com buys second-hand power supplies online.
// The following code is not original from Little Elephant Academy. Python courses.
import turtle
spiral = turtle.Turtle ()
for i in range(20):
spiral.forward(i * 10)
spiral.right(144)
turtle.done()
============================================
import turtle
painter = turtle.Turtle()
painter.pencolor(“blue”)
for i in range(50):
painter.forward(100)
painter.left(123)
turtle.done()
============================================
On the ucloud side:
0. Ask the project
1. How to check memory overflow in java (jvm \ jps \ jconsole \ jmap and other tools), what happens if the program fails
Check where there is an error
2. Under linux, how to judge whether the script starts normally after calling the shell script. Use netstat to view
3. The difference between threads and processes
4. Talk about the definition of binary sorting tree
5. Say a sort of three or more. . . What is the time complexity of quick sort. . . emmm
6. TCP three-way handshake connection
7. Have you used docker?
8. The team has a contradiction and how to solve it
9. Compare list and map
10. What are some data structures commonly used in java. .
11. How to learn new technology in peacetime
12. Why do you engage in C? Is C ++ used much?
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tcp three-way handshake connection
Feeling messy now, interviewing the network, database, operation and maintenance. The desktop didn't have time to repair, and I didn't buy any accessories today. I interviewed a few and did not win. General summary points:
1. The network does not understand routing protocols, and companies that outsource telecommunications need this technology; Ucloud also needs it. Qinhuai is still the previous OSPF, but the specific DR and the like do not understand.
2. Interview Ucloud today, Question 1: Why does the computer room need WDM? WDM principle?
Why use wavelength division multiplexing technology in optical fiber communication system
================================================
Reprinted from Baidu knows that
wavelength division multiplexing is to convert multiple channels of light into one channel of optical signal transmission, which can save fiber for long-distance transmission.
=================================================
Reprinted Known from Baidu is
mainly to save optical fiber, no need to lay fiber optic cable, and the expansion and upgrade is fast, usually two points can be installed in one day. On the basis of the original two-core fiber, a set of 40-channel wavelength division can run 40 channels of business, each channel is 400G. Specific solutions should be formulated according to the actual situation.
(1) Saving optical fiber
(2) Fast expansion speed
(3) The wavelength division of 40 channels is 400G. Usually 1 wave is 10G.
WDM wavelength division multiplexing is
a mixed transmission of different signals with different wavelengths and the
maximum use of existing optical fiber
1600G / S technology has been widely used.
Principle of wave division
================================================== =
Wavelength Division Multiplexing
The overall structure of the N-channel wavelength multiplexing WDM system mainly includes:
optical wavelength conversion unit (OTU);
wavelength division multiplexer: demultiplexer / combiner (ODU / OMU);
optical amplifier (BA / LA) / PA);
optical / electrical monitoring channel (OSC / ESC)
=====================================================
What is light put?
Optical amplifier: An optical amplifier is a subsystem product that can amplify optical signals in an optical fiber communication system.
The principle of the optical amplifier is basically based on the stimulated radiation of the laser, and the amplification effect is achieved by converting the energy of the pump light into the energy of the signal light. Since being commercialized in the 1990s, optical amplifiers have profoundly changed the status of the optical fiber communications industry.
=======================================================
What is the field of black ash production
firewall, intrusion detection and anti-virus
"The incident happened at the time of our" New Year's Day "promotion, during which a large number of coupons normally issued by the platform were consumed. The black and gray production gangs chose this time to start. Until 9 a.m. on January 20, The sum of the stolen coupons and normal coupons exceeded the platform preset threshold. The system detected anomalies and automatically found the alarm. We fixed the relevant vulnerabilities and reported the alarm as soon as possible. " Ming (pseudonym) told China Securities Journal reporter.
360-ADLab security expert Chen Zhuojian introduced to the reporter of China Securities Journal, "We call these" wool parties "who are specifically waiting for the opportunity on the Internet to" shool wool ". In order to develop quickly, it will do some activities to register and send coupons. After discovering the loophole, the gang of gangs will apply for a large number of mobile phone numbers from the code receiving platform to register to obtain coupons, and then realize cash. "
The "Wool Party" is not just about taking advantage of small profits, many of them are on the verge of breaking the law and committing crimes. Li Ming introduced, "The coupons in this incident are the types of coupons that are specially generated due to recording needs when we cooperate with Jiangsu Satellite TV's" You Are the One "program. They are only for live guests and have never appeared on the platform's normal online promotion. During the event, it was obtained by a gang of gangsters who generated a QR code scan by an abnormal method. The Shanghai police has filed a case for suspected cyber fraud. "
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Sorting out the learning idea
1, the course can be refunded. Big data or java must go through long-term study. At least half a year of study is required, otherwise the cloud computing and Beijing University Jade Bird registered before will be abandoned halfway. Actually, I didn't learn anything. This course is a protracted battle. I applied for data analysis or architect preparation at the age of 38 or 40, provided that you were still doing this at the time.
2. Learn dynamic routing protocols. OSPF and BGP, VPN, QOS.
3. Learning safety technology. Firewall, intrusion prevention, DDOS attack.
4. Don't spend too much time on interviews and resumes. Effective learning should be prioritized according to the learning plan. Ability improvement jobs are naturally easy to find, and interview questions are naturally easy to answer.
5. The same goes for good companies. Large factories or small factories, failed after the interview failed. Just keep learning.
6. There is nothing wrong with multiple interviews. You can go. When I was asked, I got the wrong answer and came back to learn again. After learning it, I'm not afraid of encountering this question again in the interview.
7. Pay attention to your image.
