compare mechanism of priority_queue of pairs

priotity_queue_of_pair.cc

#include <iostream>
#include <queue>
#include <vector>

using namespace std; 
  
typedef pair<int, int> pi; 
  
// Driver program to test methods of graph class 
int main() 
{ 
    // By default a min heap is created ordered 
    // by first element of pair. 
    priority_queue<pi, vector<pi>, greater<pi> > pq; 
  
    pq.push(make_pair(10, 20)); 
    pq.push(make_pair(20, 1)); 
    pq.push(make_pair(15, 4)); 
  
    pair<int, int> top = pq.top(); 
    cout << top.first << " " << top.second; 
    return 0; 
}