STL中的优先级队列(priority_queue)的自己实现priqueue

这篇文章主要介绍堆（最大堆和最小堆），以及一些系统对一些任务，比如线程，进程做调度的时候，所采用的优先级队列。

主要思想就是，做一个最大堆（任务的权重最大的在顶端），把顶端的任务取出，重新做一个堆，处理该任务。

// 优先级队列.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <functional>
#include <iostream>
using namespace std;

template<typename T , class FuncCmp = std::less<T> >
class priqueue
{
	T * x;
	int n;
	int maxsize;
	FuncCmp comp;
private:
	inline void swap(T & l , T & r)
	{
		T tmp = l;
		l = r;
		r = tmp;
	}

public:
	void shiftup(int end)//将满足comp的元素，从底部提到顶部
	{
		//pre :  [1,n-1]是堆
		//post : [1,n]是堆
		int i = end;
		int p = i/2;
		while( i != 1 && comp(x[i],x[p]) )
		{
			swap(x[i],x[p]);
			i = p;
			p = i / 2;
		}
	}
	void shiftdown(int end)//将不满足comp的元素，从顶部往下移
	{
		//pre :  [2,n]是堆
		//post : [1,n]是堆
		int i = 1;
		int child;
		while (1)
		{
			child = 2*i;
			if (child > end)break;
			if(child == end)
			{
				if ( !comp(x[i],x[child]) )
				{
					swap(x[i] , x[child]);
				}
				break;
			}
			if (child < end)
			{
				if ( !comp(x[child],x[child+1]) )
				{
					++child;
				}
				if ( !comp(x[i],x[child]) )
				{
					swap(x[i],x[child]);
				}
				else
				{
					break;
				}
			}
			i = child;
		}
	}
	void push_queue(T t)
	{
		if (n == maxsize)return;

		x[++n] = t;
		shiftup(n);
	}
	T pop_queue()
	{
		if(n == 0)return T();
		T ret = x[1];
		x[1] = x[n--];
		shiftdown(n);
		x[n+1] = ret;
		return ret;
	}
	void make_heap()
	{
		if(n == 0 || n==1)return;
		for (int i = 2;i<=n ; ++i)
		{
			shiftup(i);
		}
	}
	priqueue(int m)
	{
		maxsize = m;
		n = 0;
		x = new T[maxsize + 1];
	}
	~priqueue()
	{
		if (x)
		{
			delete x;
			x = NULL;
		}
	}
	int size()const
	{
		return n;
	}
};

struct Tasks
{
	int priority;

	struct OtherData
	{
		int data1;
		int data2;
		int data3;
		int data4;
	};
};

inline bool CompareTasks(Tasks * t1 , Tasks * t2)
{
	return t1->priority < t2->priority;
}

struct CompareTasksType
{
public:
	bool operator()(Tasks * t1 , Tasks * t2)
	{
		return CompareTasks(t1,t2);
	}
};

int _tmain(int argc, _TCHAR* argv[])
{
	priqueue<Tasks * , CompareTasksType> q(12);

	Tasks t1; t1.priority = 12;
	Tasks t2; t2.priority = 20;
	Tasks t3; t3.priority = 15;
	Tasks t4; t4.priority = 29;
	Tasks t5; t5.priority = 23;
	Tasks t6; t6.priority = 17;
	Tasks t7; t7.priority = 22;
	Tasks t8; t8.priority = 35;
	Tasks t9; t9.priority = 40;
	Tasks t10; t10.priority = 26;
	Tasks t11; t11.priority = 51;
	Tasks t12; t12.priority = 19;

	q.push_queue(&t1);
	q.push_queue(&t2);
	q.push_queue(&t3);
	q.push_queue(&t4);
	q.push_queue(&t5);
	q.push_queue(&t6);
	q.push_queue(&t7);
	q.push_queue(&t8);
	q.push_queue(&t9);
	q.push_queue(&t10);
	q.push_queue(&t11);
	q.push_queue(&t12);

	//q.push_queue(12);
	//q.push_queue(20);
	//q.push_queue(15);
	//q.push_queue(29);
	//q.push_queue(23);
	//q.push_queue(17);
	//q.push_queue(22);
	//q.push_queue(35);
	//q.push_queue(40);
	//q.push_queue(26);
	//q.push_queue(51);
	//q.push_queue(19);

	while(q.size() != 0)
	{
		Tasks * pT = q.pop_queue();
		//do this task
		//...
		cout<<(pT->priority)<<endl;
	}

	return 0;
}