C++ Priority Queue Size

In the C++ programming language, a priority queue is a type of container adapter. The approach in the priority queue differs from a typical queue in which elements are ordered based on First-In-First-Out (FIFO), since elements in a priority queue are processed according to their priority.

In C++, a priorityqueue is set as a max heap by default, which provides a guarantee that the highest element will be at the top of the queue. The size function of the priorityqueue class is commonly utilized to determine the total number of elements currently stored in the priority queue.

The C++ priorityqueue size function is used to get the size of the priority queue container. It returns the size as an integer value. In C++ , priorityqueue is implemented using a heap (by default, a max-heap).

Syntax:

It has the following syntax:

pq.size();

• ✅ Parameter: It does not take any parameters.
• ✅ Return Value: It returns the size of the priority queue.
• ✅ Time Complexity: It takes only O(1) time complexity, because the container keeps track of its size internally.

C++ Priority_queue::size Simple Example

Let us take an example to illustrate the priority_queue::size function in C++.

Example

#include <iostream>  

#include <queue>  

using namespace std;    //using standard namespace

int main()    //main function

{  

 priority_queue<char> mp;  

mp.push('c');  

mp.push('d');  

mp.push('a');  

mp.push('b');  

mp.push('e');  

cout<<mp.size();  

return 0;  

}

Output:

Explanation:

In this example, we create a priority_queue of characters that contains five elements (c, d, a, b, e). As the size function returns the total number of elements present in the container, the output is 5, which is the total size of stored elements.

C++ Example to calculate the sum of elements using priority_queue::size Function

Let us take an example to illustrate how to calculate the sum of elements using priority_queue::size function in C++.

Example

#include <iostream>  

#include <queue>  

using namespace std;    //using standard namespace

int main()   //main function

{  

int sum = 0;  

 priority_queue<int> pqueue;  

pqueue.push(8);  

pqueue.push(6);  

pqueue.push(3);  

pqueue.push(2);  

pqueue.push(1);  

while (pqueue.size() > 0)  

{  

sum = sum + pqueue.top();  

pqueue.pop();  

 }  

cout<< sum;  

return 0;  

}

Output:

Explanation:

In this example, we have taken a priority_queue and inserted several elements. After that, we use the size function in the loop condition to process elements until the queue becomes empty. Each iteration adds the top element (using the highest priority) to the sum and removes it. Finally, it displays the total sum of all elements.

Use Cases of priority_queue::size

There are several use cases of the priority_queue::size in C++. Some of them are as follows:

• ✅ In C++, we can use the size method to check if the queue has grown large enough before doing something.
• ✅ The size method can be used to control periodic processing until all elements of the queue are completely processed, or until it is empty.
• ✅ It can also be used to monitor the number of pending tasks in the system for cases such as job scheduling.
• ✅ We can use the size method to print the number of elements while a program is executing, for developers to observe execution.

Conclusion

In conclusion, the priority_queue::size function in C++ is a simple but useful tool for determining how many elements the container currently contains. The size function has included the feature operating in constant time (O(1)), which provides an efficient and uniform means of obtaining the size of the queue even if the collection contains a large number of items. It does not modify the contents and works efficiently in constant time, which makes it an essential part of priority queue operations.

C++ priotity_queue::size FAQs

1) What is priority_queue::size used for in C++?

In the C++ programming language, the size function returns the number of elements stored in the priority queue. It does not change the container in any way, but simply provides us with information about its size. It is very useful when we are checking to see how many items we have yet to process.

2) Does calling size affect the contents of the priority queue in C++?

No. Calling size does not change or remove any elements from the priority queue. It is a constant function that just gets a count of the elements. We can safely call size without worrying about changing the underlying structure of the container.

3) What is the time complexity of priority_queue::size in C++?

The time complexity of priority_queue::size is O(1), which means it completes in constant time. It will always take the same amount of time to compute the size, regardless of how many elements are present. It is such a fast and efficient method to use, even when handling larger data sets.

4) In what ways does size differ from empty in a priority queue?

The function size describes the actual number of elements, and empty only describes whether the container is empty or non-empty. In an example, if size returns 0, empty will return true.

5) Does size have the same applicability and utility in priority queues configured as either max heaps or min heaps in C++?

Yes, size has the same function regardless of whether the priority queue has been configured as a max priority queue or a min priority queue. It only returns the number of elements, and not the ordering or prioritization of the elements. Only top and pop are affected by being in a heap, and size does not affect the method to determine the number of elements in the queue.