【C++】vector的使用与题目练习

一、前言

学习完string类之后，我们在来学习vector难度并没有之前那么高，更加容易理解一些接口

vector是表示可变大小数组的序列容器 ，本质讲，vector使用动态分配数组来存储它的元素。

同理，对于vector的使用，我们也要学会去看文档：vector官方文档

本文重点只介绍一些常用的接口

---

二、构造函数

构造函数的具体介绍直接前往官网查看文档即可，这里只做简单介绍：

对于构造函数，这些与string类似，我们就不在多说，直接上手代码：

void Test()
{
	vector v;//无参构造
	vector v1(5, 1);//构造并初始5个1
	vector v2(v1);//拷贝构造
	vector v3(++v1.begin(), --v1.end());//迭代器初始化构造
}
1
2
3
4
5
6
7

此外，对于vector和string的关系是无法替代的，string类中有一个接口c_str()，转化成C语言的字符串要以\0结尾，所以string类最后会有一个\0,在操作上+=,<<,>>等。而vector是保存字符的动态数组，不会以\0结尾，不保存\0，且vector是T泛型，所以并不存在谁替代谁。

---

三、遍历

1.[]

void Test1()
{
	vector v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(3);
	v.push_back(4);
	for (size_t i = 0; i < v.size(); i++)
	{
		//可读可写
		v[i]++;
		cout << v[i] << endl;
	}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14

2.迭代器、范围for()

正向迭代器和反向迭代器

void Test2()
{
	vector v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(3);
	v.push_back(4);
	
	vector::iterator it = v.begin();
	while (it != v.end())
	{
		(*it)++;
		cout << *it << " ";
		it++;
	}
	cout << endl;

	vector::reverse_iterator rit = v.rbegin();
	while (rit != v.rend())
	{
		(*rit)--;
		cout << *rit << " ";
		rit++;
	}
	cout << endl;

}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

迭代器很自然和范围for联系起来：

for (auto e : v)
{
	cout << e << " ";
}
cout << endl;
1
2
3
4
5

---

四、增删查改

1.常用接口

resize&&reserve&&扩容问题

前三个比较容易理解，我们就不说了，我们直接来看resize

void Test3()
{
	vector v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(3);
	v.push_back(4);
	v.push_back(5);
	cout << v.size() << endl;
	cout << v.capacity() << endl;
	v.resize(4);
	cout << v.size() << endl;
	cout << v.capacity() << endl;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14

对于reserve:

void Test4()
{
	vector v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(3);
	v.push_back(4);
	v.push_back(5);
	cout << v.size() << endl;
	cout << v.capacity() << endl;
	v.reserve(100);
	cout << v.size() << endl;
	cout << v.capacity() << endl;
	v.reserve(50);
	cout << v.size() << endl;
	cout << v.capacity() << endl;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

capacity扩容问题：

capacity的代码在vs和g++下分别运行会发现，vs下capacity是按1.5倍增长的，g++是按2倍增长的

void Test5()
{
	size_t sz;
	std::vector foo;
	sz = foo.capacity();
	std::cout << "making foo grow:\n";
	for (int i = 0; i < 100; ++i) {
		foo.push_back(i);
		if (sz != foo.capacity()) {
			sz = foo.capacity();
			std::cout << "capacity changed: " << sz << '\n';
		}
	}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14

VS下：

Linux的g++下：

2.增删查改

1.push_back和pop_back的用法比较简单：

void Test6()
{
	vector v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(3);
	v.push_back(4);
	v.push_back(5);
	for (auto e:v)
	{
		cout << e << " ";
	}
	cout << endl;
	v.pop_back();
	v.pop_back();
	for (auto e : v)
	{
		cout << e << " ";
	}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

2.find

注意：算法库中给我们提供一个模板，vector本身并没有find接口，下面我们来看一看：

void Test7()
{
	vector v;
	v.push_back(10);
	v.push_back(20);
	v.push_back(30);
	v.push_back(40);
	v.push_back(50);
	vector::iterator pos = find(v.begin(), v.end(), 30);
	//auto pos = find(v.begin(), v.end(), 30);
	if (pos != v.end())
	{
		cout << "找到了" << endl;
	}
    else
    {
        cout<<"没找到"<

void Test8()
{
	vector v;
	v.push_back(10);
	v.push_back(20);
	v.push_back(30);
	v.push_back(40);
	v.push_back(50);
	v.insert(v.begin(), 111);
	vector::iterator pos = find(v.begin(),v.end(), 30);
	if (pos != v.end())
	{
		v.insert(pos, 70);
	}
	for (auto e : v)
	{
		cout << e << " ";
	}
	cout << endl;
	pos = find(v.begin(), v.end(),70);
	if (pos != v.end())
	{
		v.erase(pos);
	}
	for (auto e : v)
	{
		cout << e << " ";
	}
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29

void Test9()
{
	vector v;
	v.push_back(1);
	v.push_back(2);
	v.push_back(3);
	vector swapv;
	swapv.swap(v);
	cout << "v data:";
	for (size_t i = 0; i < v.size(); ++i)
		cout << v[i] << " ";
	cout << endl;
	cout << "swapv data:";
	for (size_t i = 0; i < swapv.size(); ++i)
		cout << swapv[i] << " ";
	cout << endl;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17

#include 
#include 
using namespace std;
int main(void)
{
	vectorarray;
	array.push_back(100);
	array.push_back(300);
	array.push_back(300);
	array.push_back(300);
	array.push_back(300);
	array.push_back(500);
	vector::iterator itor;
	for (itor = array.begin(); itor != array.end(); itor++)
	{
		if (*itor == 300)
		{
			itor = array.erase(itor);
		}
	}
	for (itor = array.begin(); itor != array.end(); itor++)
	{
		cout << *itor << " ";
	}
	return 0;
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

class Solution {
public:
    vector> generate(int numRows) {
        vector> vv;
        vv.resize(numRows);
        for(size_t i = 0;i