![]() Abstractly, a heap is a binary tree in which the value associated with every node is smaller than or equal to the value associated with either child node. The example program described in Section 11.3 illustrates this use.Ī priority_queue is implemented by internally building a data structure called a heap. Instead of iterating over values, a typical algorithm that uses a priority_queue constructs a loop, which repeatedly pulls values from the structure (using the top() and pop() member functions) until the collection becomes empty (tested using the empty() member function). In cases where performance or memory consumption is important, you should try both underlying containers and compare the results.īecause the priority_queue data structure does not itself know how to construct iterators, very few of the algorithms noted in Chapter 13 can be used with priority_queues. These are, of course, generalized statements which may not apply to the problem at hand. Copying takes time, so a vector may be inefficient if the size of the priority_queue will tend to increase. ![]() However, increasing the memory allocated to a vector may require copying the elements into newly allocated space. A vector has less overhead, so may be more efficient in cases where the priority_queue will tend to remain at approximately the same size. If the number of elements will vary, a deque will use less memory when the priority_queue has few elements. The default, vector, performs quite well for most cases. When deciding whether to use a vector or deque as the underlying container, consider the data which is to be stored. Queue_five(aVector.begin(), aVector.end(), m圜omparison) ![]() Returns the number of elements in the collectionĮlements of type T must be comparable to each other, either through the use of the default less-than operator, operator and std::less ![]() Returns a reference to the smallest element in the collectionĭeletes the smallest element from the collection Apache C++ Standard Library User's Guide 11.2 The priority queue OperationsĪ specialization of the priority_queue class template holds elements of type T and implements the five operations given in Table 18: Table 18: priority_queue operations FunctionĪdds a new value to the collection being maintained ![]()
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