2025.1.22笔记map/multimap

2025.1.22笔记map/multimap

一.map的定义

1.头文件

#include 

2.定义

map;

3.对组容器pair

pair可以存储两个元素，也被称作“对组”

pair主要的两个成员变量是first和second, first和second可以是任意类型，也可以是自定义的struct类型

1.定义

pairp;

2.函数列表

first () 访问对组的第一个元素。
secend() 访问对组的第二个元素。
make_pair()  生成新的pair对象。

3.创建

pairp=("jack",10);
pairp=make_pair("jack",10);

4.访问

string name=p.first;
int age=p.second;

4.给map赋值

//1.
mapm;
m[1] = "张三";//相当于定义了一个key为int，value为string的map容器 
cout << m[1] << endl;
//2.插入键值对
mapm1;//pair定义了一个键值对，对应 map的key和value
m1.insert(pair("jack", 10));
//3.拷贝
mapm2(m1);
//4.赋值
mapm3;
m3 = m1;

5.遍历

void test1(map& m)//遍历
{
	for (map::iterator it = m.begin();      it != m.end(); it++)
	{
		cout << "key" << (*it).first << "  " 
		<< "value" << (*it).second << endl;
	}
}

6.大小和交换

size empty swap

mapm;
m[1] = "张三";
m[2] = "李四";
m[3] = "王五";
cout <<"大小为"<< m.size() << endl;
if (m.empty())cout << "不为空" << endl;
else cout << "为空" << endl;
cout << "交换前  " << m[1] << "  " << m[2] << endl;
swap(m[1], m[2]);
cout << "交换后  " << m[1] << "  " << m[2] << endl；

7.删除

mapm;
m[1] = "张三";
m[2] = "李四";
m[3] = "王五";
//1. 使用key删除
m.erase(1);//删除 key = 1的节点
//2. 使用迭代器删除
map::iterator it = m.find(2);
m.erase(it);
//3.全部删除
m.erase(m.begin(), m.end());
//4. 清空整个容器
m.clear();

8.查找和统计

find(key) count(key)//1.
mapm;
m[1] = “张三”;
m[2] = “李四”;
m[3] = “王五”;
map::iterator pos = m.find(1);
if (pos != m.end())
cout << “找到了值为 " << pos->first << " 姓名为 " << pos->second << " 的元素” << endl;
else
cout << “该元素不存在” << endl;
//2.
int num = m.count(1);
cout << “key为1的有” << num << “个” << endl;//1.
mapm;
m[1] = “张三”;
m[2] = “李四”;
m[3] = “王五”;
map::iterator pos = m.find(1);
if (pos != m.end())
cout << “找到了值为 " << pos->first << " 姓名为 " << pos->second << " 的元素” << endl;
else
cout << “该元素不存在” << endl;
//2.
int num = m.count(1);
cout << “key为1的有” << num << “个” << endl;//1.
mapm;
m[1] = “张三”;
m[2] = “李四”;
m[3] = “王五”;
map::iterator pos = m.find(1);
if (pos != m.end())
cout << “找到了值为 " << pos->first << " 姓名为 " << pos->second << " 的元素” << endl;
else
cout << “该元素不存在” << endl;
//2.
int num = m.count(1);
cout << “key为1的有” << num << “个” << endl;//1.
mapm;
m[1] = “张三”;
m[2] = “李四”;
m[3] = “王五”;
map::iterator pos = m.find(1);
if (pos != m.end())
cout << “找到了值为 " << pos->first << " 姓名为 " << pos->second << " 的元素” << endl;
else
cout << “该元素不存在” << endl;
//2.
int num = m.count(1);
cout << “key为1的有” << num << “个” << endl;

//1.
mapm;
m[1] = "张三";
m[2] = "李四";
m[3] = "王五";
map::iterator pos = m.find(1);
if (pos != m.end())
	cout << "找到了值为 " << pos->first << " 姓名为 " << pos->second << " 的元素" << endl;
else
	cout << "该元素不存在" << endl;
//2.
int num = m.count(1);
cout << "key为1的有" << num << "个" << endl;

二.排序

1.默认按key从小到大
mapm;
m[1] = "张三";
m[2] = "李四";
m[3] = "王五";
for (map::iterator it = m.begin(); it != m.end(); ++it)
cout << it->first << " " << it->second << endl;
2.默认按key从大到小
改为 map>m;

三.multimap

和map的区别

map和mulitimap的区别：

map不允许容器中有相同key值的元素；

multimap允许容器中有相同key值的元素。

四.完整代码

#include
#include
#include