Difference between revisions of "cpp/container/priority queue"
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| − | A priority queue is a container adaptor that provides constant time | + | A priority queue is a container adaptor that provides constant time lookup of the largest (by default) element, at the expense of logarithmic insertion and extraction. |
A user-provided {{tt|Compare}} can be supplied to change the ordering, e.g. using {{lc|std::greater<T>}} would cause the smallest element to appear as the {{lc|top()}}. | A user-provided {{tt|Compare}} can be supplied to change the ordering, e.g. using {{lc|std::greater<T>}} would cause the smallest element to appear as the {{lc|top()}}. | ||
Revision as of 04:27, 7 July 2015
| Defined in header <queue>
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| template< class T, |
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A priority queue is a container adaptor that provides constant time lookup of the largest (by default) element, at the expense of logarithmic insertion and extraction.
A user-provided Compare can be supplied to change the ordering, e.g. using std::greater<T> would cause the smallest element to appear as the top().
Working with a priority_queue is similar to managing a heap in some random access container, with the benefit of not being able to accidentally invalidate the heap.
Contents |
Template parameters
| T | - | The type of the stored elements. |
| Container | - | The type of the underlying container to use to store the elements. The container must satisfy the requirements of Template:concept. Additionally, it must provide the following functions with the usual semantics:
The standard containers std::vector and std::deque satisfy these requirements. |
| Compare | - | A Template:concept type providing a strict weak ordering. |
Member types
| Member type | Definition |
container_type
|
Container
|
value_type
|
Container::value_type
|
size_type
|
Container::size_type |
reference
|
Container::reference
|
const_reference
|
Container::const_reference
|
Member functions
constructs the priority_queue (public member function) | |
destructs the priority_queue (public member function) | |
| assigns values to the container adaptor (public member function) | |
Element access | |
| accesses the top element (public member function) | |
Capacity | |
| checks whether the container adaptor is empty (public member function) | |
| returns the number of elements (public member function) | |
Modifiers | |
| inserts element and sorts the underlying container (public member function) | |
| (C++11) |
constructs element in-place and sorts the underlying container (public member function) |
| removes the top element (public member function) | |
| (C++11) |
swaps the contents (public member function) |
Member objects | |
| Container c |
the underlying container (protected member object) |
| Compare comp |
the comparison function object (protected member object) |
Non-member functions
| specializes the std::swap algorithm (function template) |
Helper classes
| specializes the std::uses_allocator type trait (class template specialization) |
Example
Run this code
#include <functional> #include <queue> #include <vector> #include <iostream> template<typename T> void print_queue(T& q) { while(!q.empty()) { std::cout << q.top() << " "; q.pop(); } std::cout << '\n'; } int main() { std::priority_queue<int> q; for(int n : {1,8,5,6,3,4,0,9,3,2}) q.push(n); print_queue(q); std::priority_queue<int, std::vector<int>, std::greater<int> > q2; for(int n : {1,8,5,6,3,4,0,9,3,2}) q2.push(n); print_queue(q2); }
Output:
9 8 6 5 4 3 3 2 1 0 0 1 2 3 3 4 5 6 8 9
