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std::vector in c++

LeetCode
字数统计: 1k阅读时长: 6 min
2020/09/23 Share

std::vector in C++

Declaration of std::vector

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std::vector<int> marks;

initialization of std::vector

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std::vector<int> marks = {50, 45, 47, 65, 80};
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std::vector<int> marks;
marks = {50, 45, 47, 65, 80};

Length of std::vector

marks.size() — function

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#include <iostream>
#include <vector>

int main()
{
    std::vector<int> marks = {50, 45, 47, 65, 80};
    marks = {50, 47, 60};
    std::cout << "length of array : " << marks.size() << std::endl;
    return 0;
}

Pass a std::vector to function

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#include <iostream>
#include <vector>
using namespace std;

void printVector( const vector<int> &v ){
    for(int i = 0; i < v.size(); i++){
        cout << "v[" << i << "] = " << v[i] << endl;
//        v[2] = 4;
    }
}

int main() {
    std::cout << "Hello, World!" << std::endl;
    vector<int> v = {1,2,3,4,5,6,7};
    printVector(v);
    return 0;
}

noted from: https://www.codesdope.com/cpp-stdvector/

void printVector(const std::vector\ &n) - const is used here to prevent the compiler from making a copy of the vector and this enhances the performance. The passed vector will be n in this function as &n is the parameter of the function ‘printArray’.

Screen Shot 2020-09-23 at 23.11.10

front & back

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//usage of front;
marks.front();
//usage of back;
marks.back();

empty

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marks.empty() //if true, return 1; else return 0;

resize

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#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v1 = {5, 6};
    v1.resize(5);
    for(int i = 0; i < v1.size() ; i++)
    {
        cout << v1[i] << endl;
    }
    return 0;
}
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assign

assigns new contents to the vector and replaces its current contents all.

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#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v;
    v.assign(7, 40);  // 7 elements each of value 40
    cout << v.size() << endl;
    return 0;
}

push_back

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#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v = {4, 5, 6, 7, 8};
    v.push_back(47);

    //printing values of v
    cout << "elements of v" << endl;
    for(int i = 0; i < v.size(); i++)
    {
        cout << v[i] << endl;
    }

    return 0;
}

pop_back

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#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v = {4, 5, 6, 7, 8};
    v.pop_back();

    //printing values of v
    cout << "elements of v" << endl;
    for(int i = 0; i < v.size(); i++)
    {
        cout << v[i] << endl;
    }

    return 0;
}

reserve

This function increases the capacity of the vector if the desired number of elements is greater than the capacity of the vector.

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#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v1;
    for(int i = 0; i < 50; i++)
    {
        v1.push_back(1);
    }
    v1.reserve(100);
    cout << "capacity : " << v1.capacity() << endl;
    return 0;
}
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capacity:100

erase

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#include <iostream>
#include <vector>
#include <iterator>

using namespace std;

int main()
{
    vector<int> v1 = {4, 5, 6, 7, 8};
    vector<int> v2 = {1, 2, 3, 4, 5};

    v1.erase(v1.begin()+4);  // removing a single element at position 4
    v2.erase(v2.begin()+1, v2.begin()+3);   // removing range of elements from position 1 till 2

    //printing the values of v1
    cout << "Values of v1" << endl;
    for(int i = 0; i < v1.size(); i++)
    {
        cout << v1[i] << endl;
    }

    //printing the values of v2
    cout << "Values of v2" << endl;
    for(int i = 0; i < v2.size(); i++)
    {
        cout << v2[i] << endl;
    }
    return 0;
}
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Values of v1
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Values of v2
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clear

clear all elements of the vector.

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#include <iostream>
#include <vector>

using namespace std;

int main()
{
    vector<int> v1 = {1, 2, 3};

    vector<int> v2 = {4, 5, 6};

    v1.swap(v2);

    std::cout << "Vector v1" << endl;
    for (auto i: v1)
    {
        std::cout << i << endl;
    }

    std::cout << "Vector v2" << endl;
    for (auto i: v2)
    {
        std::cout << i << endl;
    }

    return 0;
}

Multidimensional std::vector

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#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<vector<int>>  v {{{1,2,3},{4,5,6},{7,8,9}}};
    for(int i=0; i<3; i++)
    {
        for(int j=0; j<3; j++)
        {
            cout << v[i][j] << "\t";
        }
        cout << endl;
    }
    return 0;
}
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1   2   3
4   5   6
7   8   9

Passing a multidimensional std::vector to a function

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#include <iostream>
#include <vector>
using namespace std;

void display(const std::vector<std::vector<int>> &v)
{
    for(int i=0; i<v.size(); i++)
    {
        for(int j = 0; j<v[i].size(); j++)
        {
            cout << v[i][j] << "\t";
        }
        cout << endl;
    }
}

int main()
{
    vector<vector<int>>  v {{{1,2,3},{4,5,6},{7,8,9}}};
    display(v);
    return 0;
}
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