priority_queue优先级队列

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。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。

template <class Type, class Container= vector <Type>, class Compare= less <typename Container ::value_type>>

class priority_queue

1. class Type是基础数据类型

2. class Container是默认容器为Vector

3. class Compare是指排序方式,默认是less从小到大排序

下面五个函数是常用函数：

返回队列头部元素
top()

向队头插入元素
push()

删除队头元素
pop()

判断队列是否为空
empty()

返回队列元素个数
size()

priority_queue源码

template<class _Ty, class _Container = vector<_Ty>, class _Pr = less<typename _Container::value_type> > //默认以vector为容器的
class priority_queue
{ // priority queue implemented with a _Container
public:
typedef _Container container_type;
typedef typename _Container::value_type value_type;
typedef typename _Container::size_type size_type;
typedef typename _Container::reference reference;
typedef typename _Container::const_reference const_reference;

priority_queue() : c(), comp()
{ // construct with empty container, default comparator
}

explicit priority_queue(const _Pr& _Pred) : c(), comp(_Pred)
{ // construct with empty container, specified comparator
}

priority_queue(const _Pr& _Pred, const _Container& _Cont) : c(_Cont), comp(_Pred)
{ // construct by copying specified container, comparator
make_heap(c.begin(), c.end(), comp); //参见《STL系列之四 heap 堆的相关函数》
}

template<class _Iter>
priority_queue(_Iter _First, _Iter _Last) : c(_First, _Last), comp()
{ // construct by copying [_First, _Last), default comparator
make_heap(c.begin(), c.end(), comp);
}

template<class _Iter>
priority_queue(_Iter _First, _Iter _Last, const _Pr& _Pred) : c(_First, _Last), comp(_Pred)
{ // construct by copying [_First, _Last), specified comparator
make_heap(c.begin(), c.end(), comp);
}

template<class _Iter>
priority_queue(_Iter _First, _Iter _Last, const _Pr& _Pred, const _Container& _Cont) : c(_Cont), comp(_Pred)
{ // construct by copying [_First, _Last), container, and comparator
c.insert(c.end(), _First, _Last);
make_heap(c.begin(), c.end(), comp);
}

bool empty() const
{ // test if queue is empty
return (c.empty());
}

size_type size() const
{ // return length of queue
return (c.size());
}

const_reference top() const
{ // return highest-priority element
return (c.front());
}

reference top()
{ // return mutable highest-priority element (retained)
return (c.front());
}

void push(const value_type& _Pred)
{ // insert value in priority order
c.push_back(_Pred);
push_heap(c.begin(), c.end(), comp);
}

void pop()
{ // erase highest-priority element
pop_heap(c.begin(), c.end(), comp);
c.pop_back();
}

protected:
_Container c; // the underlying container
_Pr comp; // the comparator functor
};

实现priority_queue的实例：先增加4人进队，再增加3人。按权值从小到大，字符序列从小到大排列

#include <queue>
#include <cstring>
#include <cstdio>
using namespace std;
//结构体
struct Node
{
char szName[20];
int priority;
Node(int nri, char *pszName)
{
strcpy_s(szName, pszName);
priority = nri;
}
};

//结构体的比较方法 改写operator()
class NodeCmp
{
public:
bool operator()(const Node &na, const Node &nb)
{
if (na.priority != nb.priority)
return na.priority >= nb.priority;
else
return strcmp(na.szName, nb.szName) > 0;
}
};

void PrintfNode(Node &na)
{
printf("%s %d\n", na.szName, na.priority);
}

int main()
{
//优先级队列默认是使用vector作容器，底层数据结构为堆。
priority_queue<Node, vector<Node>, NodeCmp> a;

//有4个人进入队列
a.push(Node(5, "小谭"));
a.push(Node(3, "小刘"));
a.push(Node(1, "小涛"));
a.push(Node(5, "小王"));

//再进入3个人
a.push(Node(2, "小白"));
a.push(Node(2, "小强"));
a.push(Node(3, "小新"));

//所有人都依次出队
while (!a.empty())
{
PrintfNode(a.top());
a.pop();
}

return 0;
}

以上内容可参考MSDN