Syntax of priority queue

Question

Why do we require three parameters in order to create a priority queue with user-defined comparison?

priority_queue<Node*, vector<Node*>, comp> pq;

Why can't we create our own comparison operator by writing something like priority_queue<Node*, comp> pq;(removed vectornode*>)? 

What is the function of vector<node*>?
Also, how are the elements selected for comparison and then pushed into the queue?

Answer 1

We must first include the queue header file in order to establish a priority queue in C++.

#include <queue>

Once we import this file, we can create a priority_queue using the following syntax:

priority_queue<type> pq;

In this case, type denotes the data type that will be stored in the priority queue. 

 For  example

// create a priority queue of integer type
priority_queue<int> pq_integer;

// create a priority queue of string type
priority_queue<string> pq_string;