c++ priority_queues

priority_queue 优先级队列是一个拥有权值概念的单向队列queue，在这个队列中，所有元素是按优先级排列的（也可以认为queue是个按进入队列的先后做为优先级的优先级队列——先进入队列的元素优先权要高于后进入队列的元素）。在计算机操作系统中，优先级队列的使用是相当频繁的，进线程调度都会用到。在STL的具体实现中，priority_queue也是以别的容器作为底部结构，再根据堆的处理规则来调整元素之间的位置

empty	判断是否为空
size	返回元素的数量
top	返回位于顶部的引用的元素
push	将一个元素添加到顶部
pop	删除顶部的元素

#include <queue>
#include <vector>
#include <deque>
#include <list>
#include <xfunctional>
#include <iostream>

//构造函数
void priority_queueConstructor(void);

//从priority_queue中删除顶部的元素
void priority_queue_pop(void);

//将一个元素添加到priority_queue的顶部 
void priority_queue_push(void);

//返回priority_queue元素的数量 
void priority_queue_size(void);

//返回位于priority_queue顶部的引用的元素 
void priority_queue_top(void);

int main()
{
	//priority_queueConstructor();
	//priority_queue_pop();
	//priority_queue_push();
	//priority_queue_size();
	//priority_queue_top();
	using namespace std;
	priority_queue <int> q1;
	q1.push(1);
	q1.push(2);
	q1.push(3);
	q1.push(4);
	q1.push(5);
	return 0;
}


//构造函数
void priority_queueConstructor(void)
{
	using namespace std;

	// The first member function declares priority_queue
	// with a default vector base container
	priority_queue <int> q1;
	cout << "q1 = ( ";
	while (!q1.empty())
	{
		cout << q1.top() << " ";
		q1.pop();
	}
	cout << ")" << endl;

	// Explicitly declares a priority_queue with nondefault
	// deque base container
	priority_queue <int, deque <int> > q2;
	q2.push(5);
	q2.push(15);
	q2.push(10);
	cout << "q2 = ( ";
	while (!q2.empty())
	{
		cout << q2.top() << " ";
		q2.pop();
	}
	cout << ")" << endl;

	// This method of printing out the elements of a priority_queue
	// removes the elements from the priority queue, leaving it empty
	cout << "After printing, q2 has " << q2.size() << " elements." << endl;

	// The third member function declares a priority_queue 
	// with a vector base container and specifies that the comparison 
	// function greater is to be used for ordering elements
	priority_queue <int, vector<int>, greater<int> > q3;
	q3.push(2);
	q3.push(1);
	q3.push(3);
	cout << "q3 = ( ";
	while (!q3.empty())
	{
		cout << q3.top() << " ";
		q3.pop();
	}
	cout << ")" << endl;

	// The fourth member function declares a priority_queue and
	// initializes it with elements copied from another container:
	// first, inserting elements into q1, then copying q1 elements into q4
	q1.push(100);
	q1.push(200);
	priority_queue <int> q4(q1);
	cout << "q4 = ( ";
	while (!q4.empty())
	{
		cout << q4.top() << " ";
		q4.pop();
	}
	cout << ")" << endl;

	// Creates an auxiliary vector object v5 to be used to initialize q5
	vector <int> v5;
	vector <int>::iterator v5_Iter;
	v5.push_back(10);
	v5.push_back(30);
	v5.push_back(20);
	cout << "v5 = ( ";
	for (v5_Iter = v5.begin(); v5_Iter != v5.end(); v5_Iter++)
		cout << *v5_Iter << " ";
	cout << ")" << endl;

	// The fifth member function declares and
	// initializes a priority_queue q5 by copying the
	// range v5[_First, _Last) from vector v5
	priority_queue <int> q5(v5.begin(), v5.begin() + 2);
	cout << "q5 = ( ";
	while (!q5.empty())
	{
		cout << q5.top() << " ";
		q5.pop();
	}
	cout << ")" << endl;

	// The sixth member function declares a priority_queue q6
	// with a comparison function greater and initializes q6
	// by copying the range v5[_First, _Last) from vector v5
	priority_queue <int, vector<int>, greater<int> >
		q6(v5.begin(), v5.begin() + 2);
	cout << "q6 = ( ";
	while (!q6.empty())
	{
		cout << q6.top() << " ";
		q6.pop();
	}
	cout << ")" << endl;

	return;
	/*
	q1 = ( )
	q2 = ( 15 10 5 )
	After printing, q2 has 0 elements.
	q3 = ( 1 2 3 )
	q4 = ( 200 100 )
	v5 = ( 10 30 20 )
	q5 = ( 30 10 )
	q6 = ( 10 30 )
	请按任意键继续. . .
	*/

}

//从priority_queue中删除顶部的元素
void priority_queue_pop(void)
{
	using namespace std;
	priority_queue <int> q1, s2;

	q1.push(10);
	q1.push(20);
	q1.push(30);

	priority_queue <int>::size_type i, iii;
	i = q1.size();
	cout << "The priority_queue length is " << i << "." << endl;

	const int& ii = q1.top();
	cout << "The element at the top of the priority_queue is "
		<< i << "." << endl;

	q1.pop();

	iii = q1.size();
	cout << "After a pop, the priority_queue length is "
		<< iii << "." << endl;

	const int& iv = q1.top();
	cout << "After a pop, the element at the top of the "
		<< "priority_queue is " << iv << "." << endl;

	return;
	/*
	The priority_queue length is 3.
	The element at the top of the priority_queue is 3.
	After a pop, the priority_queue length is 2.
	After a pop, the element at the top of the priority_queue is 20.
	请按任意键继续. . .
	*/
}

//将一个元素添加到priority_queue的顶部 
void priority_queue_push(void)
{
	using namespace std;
	priority_queue<int> q1;

	q1.push(10);
	q1.push(30);
	q1.push(20);

	priority_queue<int>::size_type i;
	i = q1.size();
	cout << "The priority_queue length is " << i << "." << endl;

	const int& ii = q1.top();
	cout << "The element at the top of the priority_queue is "
		<< ii << "." << endl;

	return;
	/*
	The priority_queue length is 3.
	The element at the top of the priority_queue is 30.
	请按任意键继续. . .
	*/
}

//返回priority_queue元素的数量 
void priority_queue_size(void)
{
	using namespace std;
	priority_queue <int> q1, q2;
	priority_queue <int>::size_type i;

	q1.push(1);
	i = q1.size();
	cout << "The priority_queue length is " << i << "." << endl;

	q1.push(2);
	i = q1.size();
	cout << "The priority_queue length is now " << i << "." << endl;

	return;
	/*
	The priority_queue length is 1.
	The priority_queue length is now 2.
	请按任意键继续. . .
	*/
}

//返回位于priority_queue顶部的引用的元素 
void priority_queue_top(void)
{
	using namespace std;
	priority_queue<int> q1;

	q1.push(10);
	q1.push(30);
	q1.push(20);

	priority_queue<int>::size_type i;
	i = q1.size();
	cout << "The priority_queue length is " << i << "." << endl;

	const int& ii = q1.top();
	cout << "The element at the top of the priority_queue is "
		<< ii << "." << endl;

	return;
	/*
	The priority_queue length is 3.
	The element at the top of the priority_queue is 30.
	请按任意键继续. . .
	*/
}

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