优先级队列相对于普通队列，提供了插队功能，每次最先出队的不是最先入队的元素，而是优先级最高的元素。
它的实现采用了标准库提供的heap算法。该系列算法一共提供了四个函数。使用方式如下：
首先建立一个容器，放入元素:
1 vector<int> vec; 2 insertNums(vec, 3, 7); 3 insertNums(vec, 5, 9); 4 insertNums(vec, 1, 4);
打印结果为:
all elements 3 4 5 6 7 5 6 7 8 9 1 2 3 4
然后调用make_heap()， 将容器内[begin(), end())的元素建立成堆:
make_heap(vec.begin(), vec.end());
打印结果为:
after make heap 9 8 6 7 7 5 5 3 6 4 1 2 3 4
然后我们调用pop_heap(),该算法必须保证[begin(),end())之间的元素已经是一个堆，
然后它将堆顶的元素放到最后，再将[begin(),end() - 1)内的元素重新排列成堆:
pop_heap(vec.begin(), vec.end()); vec.pop_back(); print(vec, "after pop heap");
打印结果为:
after pop heap 8 7 6 7 4 5 5 3 6 4 1 2 3
接下来调用push_heap(),该算法必须保证[begin(),end() - 1)已经是一个堆，再将整个[begin(),end())调整为一个堆:
vec.push_back(17); push_heap(vec.begin(), vec.end()); print(vec, "after push heap");
打印结果为:
after push heap 17 7 8 7 4 5 6 3 6 4 1 2 3 5
最后我们调用sort_heap(),将[begin(),end())中的元素转化为有序序列，前提是[begin(),end())已经是一个堆:
sort_heap(vec.begin(), vec.end()); print(vec, "after sort heap");
打印结果为:
after sort heap 1 2 3 3 4 4 5 5 6 6 7 7 8 17
完整的测试代码为:
#include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; template <typename T> void insertNums(T &t, int first, int last) { while(first <= last) { t.insert(t.end(), first); ++ first; } } template <typename T> void print(const T &t, const std::string &s = "") { cout << s << endl; for(typename T::const_iterator it = t.begin(); it != t.end(); ++ it) cout << *it << " "; cout << endl; } int main(int argc, char const *argv[]) { vector<int> vec; insertNums(vec, 3, 7); insertNums(vec, 5, 9); insertNums(vec, 1, 4); print(vec, "all elements"); make_heap(vec.begin(), vec.end()); print(vec, "after make heap"); pop_heap(vec.begin(), vec.end()); vec.pop_back(); print(vec, "after pop heap"); vec.push_back(17); push_heap(vec.begin(), vec.end()); print(vec, "after push heap"); sort_heap(vec.begin(), vec.end()); print(vec, "after sort heap"); return 0; }
根据以上算法，我们来实现优先级队列priority_queue，代码如下:
1 #ifndef PRIORITY_QUEUE_H 2 #define PRIORITY_QUEUE_H 3 #include <vector> 4 #include <algorithm> 5 #include <functional> 6 7 template <typename T, 8 typename Container = std::vector<T>, 9 typename Compare = std::less<typename Container::value_type> > 10 class PriorityQueue 11 { 12 public: 13 typedef typename Container::value_type value_type; 14 typedef typename Container::size_type size_type; 15 typedef Container container_type; 16 typedef value_type& reference; 17 typedef const value_type& const_reference; 18 19 PriorityQueue(const Compare &comp = Compare(), 20 const Container &cont = Container()); 21 22 23 24 template <typename InputIter> 25 PriorityQueue(InputIter first, InputIter last, 26 const Compare &comp = Compare(), 27 const Container &cont = Container()); 28 29 void push(const value_type &val) 30 { 31 _cont.push_back(val); 32 std::push_heap(_cont.begin(), _cont.end(), _comp); 33 } 34 35 void pop() 36 { 37 std::pop_heap(_cont.begin(), _cont.end(), _comp); 38 _cont.pop_back(); 39 } 40 41 bool empty() const { return _cont.empty(); } 42 size_type size() const { return _cont.size(); } 43 44 const_reference top() const { return _cont.front(); } 45 46 private: 47 Compare _comp; 48 Container _cont; 49 50 }; 51 52 template <typename T, typename Container, typename Compare> 53 PriorityQueue<T, Container, Compare>::PriorityQueue(const Compare &comp, 54 const Container &cont) 55 :_comp(comp), _cont(cont) 56 { 57 std::make_heap(_cont.begin(), _cont.end(), _comp); 58 } 59 60 61 template <typename T, typename Container, typename Compare> 62 template <typename InputIter> 63 PriorityQueue<T, Container, Compare>::PriorityQueue(InputIter first, InputIter last, 64 const Compare &comp, 65 const Container &cont) 66 :_comp(comp), _cont(cont) 67 { 68 _cont.insert(_cont.end(), first, last); 69 std::make_heap(_cont.begin(), _cont.end(), _comp); 70 } 71 72 #endif
测试代码如下:
1 #include "priority_queue.hpp" 2 #include <iostream> 3 using namespace std; 4 5 int main(int argc, const char *argv[]) 6 { 7 PriorityQueue<float> q; 8 q.push(66.6); 9 q.push(22.3); 10 q.push(44.4); 11 12 cout << q.top() << endl; 13 q.pop(); 14 cout << q.top() << endl; 15 q.pop(); 16 q.push(11.1); 17 q.push(55.5); 18 q.push(33.3); 19 q.pop(); 20 21 while(!q.empty()) 22 { 23 cout << q.top() << " "; 24 q.pop(); 25 } 26 cout << endl; 27 28 29 30 return 0; 31 }
测试结果为:
66.6 44.4 33.3 22.3 11.1
原文：http://www.cnblogs.com/gjn135120/p/4007429.html