std::priority_queue
From cppreference.com
Defined in header <queue>
|
||
template< class T, |
||
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.
Template parameters
T | - | The type of the stored elements. The behavior is undefined if T is not the same type as Container::value_type . (since C++17)
|
Container | - | The type of the underlying container to use to store the elements. The container must satisfy the requirements of SequenceContainer , and its iterators must satisfy the requirements of RandomAccessIterator . Additionally, it must provide the following functions with the usual semantics:
The standard containers std::vector and std::deque satisfy these requirements. |
Compare | - | A Compare type providing a strict weak ordering.
|
Member types
Member type | Definition |
container_type
|
Container |
value_compare (C++17)
|
Compare
|
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 underlying container 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) | |
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 (function template) |
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 : {1,8,5,6,3,4,0,9,7,2}) q.push(n); print_queue(q); std::priority_queue<int, std::vector<int>, std::greater<int> > q2; for(int n : {1,8,5,6,3,4,0,9,7,2}) q2.push(n); print_queue(q2); // Using lambda to compare elements. auto cmp = [](int left, int right) { return (left ^ 1) < (right ^ 1);}; std::priority_queue<int, std::vector<int>, decltype(cmp)> q3(cmp); for(int n : {1,8,5,6,3,4,0,9,7,2}) q3.push(n); print_queue(q3); }
Output:
9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 8 9 6 7 4 5 2 3 0 1