Introduction

There were two phone interviews in the early selection phase, which I’ll skip here. First published at: https://www.jianshu.com/p/d5aa63a27172

First Interview

Chengdu, April 11

• Introduce your projects, what were the difficulties, and how did you solve them
• Introduce C++11 features
• Explain the fork function
• Explain the TIME_WAIT state
• Why does a TCP connection handshake require three steps
• Explain iterator invalidation. Does push_back cause iterator invalidation?
• Characteristics of red-black trees, explain
• Methods to resolve hash collisions
• Differences between processes and threads
• What thread models do you use
• Explain coroutines
• Explain the quicksort algorithm
• What is a stable sort, is quicksort stable, and why
• Derive the formula for the worst-case scenario of quicksort
• Why should a destructor be virtual
• Why can’t a constructor be a virtual function
• Questions printed on paper, testing: new[] objects, static members, what exactly a subclass constructor calls, differences between copy constructors and assignment operators, when the equals sign appears in a copy constructor, when an assignment operator is needed, deep copy vs. shallow copy, when virtual functions are called.

Below is one of the questions, please write the output:

#include <iostream>
using namespace std;

struct A{
    A(){
        local_var++;
    }
    virtual void func(){
        cout << "A" << endl;
    }
    static int local_var;
};

int A::local_var = 0;

struct B : A{
    B(){
        local_var+=2;
    }
    virtual void func(){
        cout << "B" << endl;
    }
};

int main(){
    A* a1 = new B[3]; 
    cout << a1[0].local_var << endl;
    a1->func();
    A a2 = a1[0];
    cout << a2.local_var << endl;
    a2.func();
    A a3;
    a3 = a1[0];
    cout << a3.local_var << endl;
    a3.func();
}

What problem will occur in the following code?

#include <iostream>
using namespace std;

struct A{
    virtual void func1(){
        cout << a << endl;
    }
    void func2(){
        cout << a << endl;
    }
    void func3(){
        cout << "a" << endl;
    }
    int a;
};

int main(){
    A * a = (A*)malloc(sizeof(A));
    a->func1();
    a->func2();
    a->func3();
}

• The approach to a problem during the written test (previous Nowcoder test. The interviewer actually printed all my test answers and results, including multiple-choice and algorithm questions, how many times I submitted, how many times I failed). Testing when the virtual pointer is initialized.
• Randomly selected a question on paper. Given preorder traversal ABC and postorder traversal CBA, what is the inorder traversal? Draw out the two possible scenarios.
• The approach to the first algorithm question during the written test (previous Nowcoder test)
• There are 100 marbles, two players take turns, each person can only take 1-5 marbles, the person who cannot take any loses, what is the winning strategy?
• What have you been learning recently (server programming)? What did you learn before (TensorFlow)? How did you learn it? What do you think about TensorFlow’s powerful neural networks?
• Family situation.
• After leaving, wrote code in the lobby: find elements in char array a that are not in char array b, and put them in char array c. Here I forgot to convert char characters to unsigned char type.

Second Interview

Chengdu, April 13

• Self-introduction
• What are system calls? Which system calls have you used? Which system calls take a long time?
• Have you used gdb debugging? What is a conditional breakpoint?
• Difference between function pointers and pointer functions. Write an example.
• Write a fork call example by hand. In what situations have you used fork calls?
• Explain the connect function in UDP.
• What is an index? Is adding more indexes always better? (I admitted to looking at interview experiences for the index question, but came up with the follow-up question myself)
• Which questions from the last interview did you research afterward?
• There was a problem with your code in the last interview, do you know what it was?
• Where did you learn the answers to these questions? What have you been doing these two days?
• Some suggestions for you: look into gdb debugging, database knowledge, network programming, and practice more.

Aftermath

Received a phone call on April 20 confirming the offer from Tencent.