map/multimap容器及STL案例

1.map概念：map中所有元素都是pair

pair中的第一个元素为key（键值）起到索引作用，第二个为value（实值）

所有元素都会根据key值自动排序

本质：map/multimap属于关联式容器，底层结构是用二叉树实现

优点：可以根据key值快速找到value值

map和/multimap区别：是否允许有相同的key值（都允许有重复的value值）

2.map的构造和赋值

 

void PrintMap(map<int, int>& m)
{
	for (map<int, int>::iterator it = m.begin(); it != m.end(); it++)
	{
		cout << "key值= " << it->first << " value值=" << (*it).second << endl;
	}
	cout << endl;
}
void test01()
{
	map<int, int> m1;
	m1.insert(pair<int, int>(1, 10));//匿名队组实现插入
	m1.insert(pair<int, int>(2, 20));//插入按照key值自动排序
	m1.insert(pair<int, int>(4, 40));
	m1.insert(pair<int, int>(3, 30));
	m1.insert(pair<int, int>(5, 50));
	PrintMap(m1);
	map<int, int> m2(m1);//拷贝构造
	PrintMap(m2);
	map<int, int> m3;
	m3 = m1;
	PrintMap(m3);//operator=赋值
}

3.map容器的大小和交换

 4.map容器中插入和删除

 

void PrintMap(map<int, int>& m)
{
	for (map<int, int>::iterator it = m.begin(); it != m.end(); it++)
	{
		cout << "key值= " << it->first << " value值=" << (*it).second << endl;
	}
	cout << endl;
}
void test01()
{
	map<int, int> m1;
	m1.insert(pair<int, int>(1, 10));//匿名队组实现插入
	m1.insert(make_pair(2, 20));//用make_pair实现
	m1.insert(map<int, int>::value_type(3, 30));//用value_type实现
	m1[4] = 40;//用[]实现;
	cout << m1[5] << endl;//不建议用[]访问，如果不存在会自动插入<5,0>
	PrintMap(m1);
	m1.erase(m1.begin());//迭代器删除
	PrintMap(m1);
	m1.erase(2);//按照key值删除
	PrintMap(m1);
	//清空
	//m1.erase(m1.begin(), m1.end());//按照区间删除
	//PrintMap(m1);
	m1.clear();
	PrintMap(m1);
}

5.map容器的查找和统计

6.map容器的排序操作

 默认按照key值从小到大排序，用仿函数可以自定义排序规则

class MyCompare
{
public:
	bool operator()(int v1,int v2) const//仿函数
	{
		return v1 > v2;//比较的是两个队组的key值
	}
};
void test01()
{
	map<int, int,MyCompare> m1;
	m1.insert(pair<int, int>(1, 10));//匿名队组实现插入
	m1.insert(pair<int, int>(2, 20));//插入按照key值自动排序
	m1.insert(pair<int, int>(4, 40));
	m1.insert(pair<int, int>(3, 30));
	m1.insert(pair<int, int>(5, 50));
	for (map<int, int, MyCompare>::iterator it = m1.begin(); it != m1.end(); it++)
	{
		cout << "key值=" << it->first << " value=" << it->second << endl;
	}
}

7.STL案例，员工分组

class Worker
{
public:
	string m_name;
	int m_salary;
};
//创建员工
void CreatPerson(vector<Worker>& v)
{
	string PersonSeed = "ABCDEFGHIJ";
	for (int i = 0; i < 10; i++)
	{
		Worker worker;//注意要先创建员工再插入vector容器
		string name = "员工";
		name += PersonSeed[i];
		worker.m_name = name;
		worker.m_salary = rand() % 10000 + 10000;//10000--19999
		v.push_back(worker);
	}
}
//员工分组
void SetGroup(vector<Worker>& v,multimap<int,Worker> &m)
{
	for (vector<Worker>::iterator it = v.begin(); it != v.end(); it++)
	{
		//产生随机部门编号
		int depid = rand() % 3;//0 1 2
		m.insert(make_pair(depid, *it));
	}
}
//打印员工信息
void PrintWorker(multimap<int, Worker>& m)
{
	multimap<int,Worker>::iterator pos=m.find(0);
	int num = m.count(0);
	cout << "策划部门：" << endl;
	for (int i = 0; i < num&&pos!=m.end(); pos++,i++)
	{
		cout << "员工部门：" << pos->first << " 姓名：" << (pos->second).m_name << " 员工薪资：" << (pos->second).m_salary << endl;
	}
	cout << "------------------------------------------------" << endl;
	pos = m.find(1);
	num = m.count(1);
	cout << "美术部门：" << endl;
	for (int i = 0; i < num && pos != m.end(); pos++,i++)
	{
		cout << "员工部门：" << pos->first << " 姓名：" << (pos->second).m_name << " 员工薪资：" << (pos->second).m_salary << endl;
	}
	cout << "------------------------------------------------" << endl;
	pos = m.find(2);
	num = m.count(2);
	cout << "研发部门：" << endl;
	for (int i = 0; i < num && pos != m.end(); pos++,i++)
	{
		cout << "员工部门：" << pos->first << " 姓名：" << (pos->second).m_name << " 员工薪资：" << (pos->second).m_salary << endl;
	}
	cout << "------------------------------------------------" << endl;
}
void test01()
{
	srand((unsigned int)time(NULL));//随机数种子
	vector<Worker> vWorker;//存储员工的vector容器
	//1.创建员工
	CreatPerson(vWorker);
	multimap<int, Worker> mWorker;//key值为员工部门编号，value值为员工
	//2.员工分部门
	SetGroup(vWorker,mWorker);
	//3.显示员工及其部门
	PrintWorker(mWorker);
}