vector Usage

介绍

在c++中，vector像是一种动态数组，可以自由更改大小，有时候也被称为容器。
使用vector前需要包含#include <vector>头文件

使用方法

初始化

int是指容器的类型，abc是容器的名称。

vector<int>abc;

常用内置函数

//b为向量，将b的0-2个元素赋值给向量a
a.assign(b.begin(),b.begin()+3);
//a含有4个值为2的元素
a.assign(4,2);
//返回a的最后一个元素
a.back();
//返回a的第一个元素
a.front();
//返回a的第i元素,当且仅当a存在
a[i];
//清空a中的元素
a.clear();
//判断a是否为空，空则返回true，非空则返回false
a.empty();
//删除a向量的最后一个元素
a.pop_back();
//删除a中第一个（从第0个算起）到第二个元素，也就是说删除的元素从a.begin()+1算起（包括它）一直到a.begin()+3（不包括它）结束
a.erase(a.begin()+1,a.begin()+3);
//在a的末尾插入一个元素，其值为i
a.push_back(i);
//在a的第一个元素（从第0个算起）位置插入数值5,
a.insert(a.begin()+1,5);
//在a的第一个元素（从第0个算起）位置插入3个数，其值都为5
a.insert(a.begin()+1,3,5);
//b为数组，在a的第一个元素（从第0个元素算起）的位置插入b的第三个元素到第5个元素（不包括b+6）
a.insert(a.begin()+1,b+3,b+6);
//返回a中元素的个数
a.size();
//返回a在内存中总共可以容纳的元素个数
a.capacity();
//将a的现有元素个数调整至10个，多则删，少则补，其值随机
a.resize(10);
//将a的现有元素个数调整至10个，多则删，少则补，其值为2
a.resize(10,2);
//将a的容量扩充至100，
a.reserve(100);
//b为向量，将a中的元素和b中的元素整体交换
a.swap(b);
//b为向量，向量的比较操作还有 != >= > <= <
a==b;

常用算法

#include<algorithm>
//对a中的从a.begin()（包括它）到a.end()（不包括它）的元素进行从小到大排列
sort(a.begin(),a.end());
//对a中的从a.begin()（包括它）到a.end()（不包括它）的元素倒置，但不排列，如a中元素为1,3,2,4,倒置后为4,2,3,1
reverse(a.begin(),a.end());
 //把a中的从a.begin()（包括它）到a.end()（不包括它）的元素复制到b中，从b.begin()+1的位置（包括它）开始复制，覆盖掉原有元素
copy(a.begin(),a.end(),b.begin()+1);
//在a中的从a.begin()（包括它）到a.end()（不包括它）的元素中查找10，若存在返回其在向量中的位置
 find(a.begin(),a.end(),10);

Introduction

In C++, a vector is like a dynamic array that can change its size freely and is sometimes referred to as a container.
To use vector, you need to include the #include <vector> header file.

Usage

Initialization

int refers to the type of the container, and abc is the name of the container.

vector<int>abc;

Common Built-in Functions

//b is a vector, assign the first 3 elements of b to vector a
a.assign(b.begin(),b.begin()+3);
//a contains 4 elements with value 2
a.assign(4,2);
//return the last element of a
a.back();
//return the first element of a
a.front();
//return the i-th element of a, if a exists
a[i];
//clear all elements in a
a.clear();
//check if a is empty, return true if empty, false otherwise
a.empty();
//delete the last element of vector a
a.pop_back();
//delete elements from the first (index 0) to the third element of a, meaning it deletes elements starting from a.begin()+1 (inclusive) up to a.begin()+3 (exclusive)
a.erase(a.begin()+1,a.begin()+3);
//insert an element with value i at the end of a
a.push_back(i);
//insert value 5 at the first element position (from index 0) of a
a.insert(a.begin()+1,5);
//insert 3 numbers, all with value 5, at the first element position (from index 0) of a
a.insert(a.begin()+1,3,5);
//b is an array, insert the third to the fifth element of b (excluding b+6) at the first element position (from index 0) of a
a.insert(a.begin()+1,b+3,b+6);
//return the number of elements in a
a.size();
//return the total number of elements a can hold in memory
a.capacity();
//adjust the existing number of elements in a to 10, deleting excess or filling with random values
a.resize(10);
//adjust the existing number of elements in a to 10, deleting excess or filling with value 2
a.resize(10,2);
//expand the capacity of a to 100
a.reserve(100);
//b is a vector, swap all elements between a and b
a.swap(b);
//b is a vector, comparison operations for vectors also include != >= > <= <
a==b;

Common Algorithms

#include<algorithm>
//sort the elements in a from a.begin() (inclusive) to a.end() (exclusive) in ascending order
sort(a.begin(),a.end());
//reverse the elements in a from a.begin() (inclusive) to a.end() (exclusive), but do not sort. Example: if a contains 1,3,2,4, after reversal it becomes 4,2,3,1
reverse(a.begin(),a.end());
 //copy elements from a.begin() (inclusive) to a.end() (exclusive) in a to b, starting at position b.begin()+1 (inclusive), overwriting existing elements
copy(a.begin(),a.end(),b.begin()+1);
//search for 10 in elements from a.begin() (inclusive) to a.end() (exclusive) in a, return its position in the vector if found
 find(a.begin(),a.end(),10);