Didi CTO Five rounds of interviews is really exciting, I saw many aspects of the experience before is extremely difficult, I feel lucky, Although the interview is quite difficult, the interviewers are not bad. And the results will be available immediately after the interview, which is very exciting!

This article is shared with friends who need to interview questions, and I wish everyone to successfully get the offer they want.

September 9, 1:00 p.m.

While introducing

yourself + introducing

the

difficulties and solutions

in the project project Java

thread state

and

transitionJava The way to create threads

What are

the

classes under the JUC package, and how much can you say about

ReentranLock with The difference between sychronized

volitile’s memory semantics, how to implement the underlying

explanations happens-before, what are the rules

CurrentHashMap source code

MySQL index and differentiation

algorithm problem: Print the matrix

clockwise September 10 at 1:00 p.m. Two-sided,

Mainly deep excavation projects (45min)
Introduce

the project, the difficulties in the project (15min)

how MySQL is optimized, how much data

is the difference between inverted

indexes and positive indexes

ElasticSearch principle (inverted index + TF/IDF)

Zookeeper has used,

introduce

what scenarios Zookeeper is generally used in addition to the

ZAB protocol, In introducing several reject strategies of several distributed consistency protocol (Paxos, Raft)

thread pools and their application scenariosWhat

are

the

LSM-tree applications in those scenarios, advantages and disadvantages

of the intended work? Big data or development and

writing SQL: query the top five students and grades

in each class September 12, 3:00 p.m

. Three sides

did not ask about technology, talk about life (40min)

What do you know about Didi, do you know our technology stack?

There are still a few questions I don’t remember about

big data or development~

September 14, 3:00 p.m. Introduce yourself on all sides

, the

project asks

what Java collection classes are commonly used, and the difference between ArrayList and LinkedList;

HackMap underlying implementation, why scaling is a power of 2;

If you want thread safety, how

to

use the JUC package to understand which classes, synchronized and JDK provide locks difference;

CAS principle, ABA problem; Let’s talk about the lock upgrade process;

volatile talks about why the atomic

JVM memory model cannot be guaranteed, what regions are there in the Cenozoic, and what is the role;

How to determine whether an object can be recycled (1 reference counting 2 reachability analysis)

JVM common garbage collection algorithm, talk about the CMS principle

Redis common data structure; Ordered collection underlying implementation;

Find out how ranking is achieved at the bottom; How to implement distributed locks with Redis, problems and solutions that may be encountered

and

find a dichotomy on

September 16 at 3:00 p.m. Five-sided

self-introduction, project questions

and chat network, TCP 3 handshake process, whether the third time can carry data, how to avoid SYN attacks (syncookies);

TCP waves four times to say, why wait for 2MSL, if the second and third waves can be merged (yes).

operating system, the difference between processes, threads and coroutines;

What is the problem if many threads are created;

What are the interprocess communication methods How MySQL

indexes are implemented, why use B+ trees instead of B-tree binary trees;

the difference between clustered and non-clustered indexes; How to do index optimization in normal times, the leftmost matching principle;

Your strengths, your weaknesses (the interviewer said that we have the same shortcomings

)

You recently read a technical book, I mentioned “The Art of Java Concurrent Programming” read it three times, the interviewer asked me to talk in detail about each chapter what

do you

think about the Internet industry

What

will you do if your performance is beaten C (This is a big hole ~)

Summary:

I wish you all the best offers.