How can I create Min stl priority_queue?

Question

The default stl priority queue is a Max one (Top function returns the largest element).

Say, for simplicity, that it is a priority queue of int values.

Answer 1

In C++11 you could also create an alias for convenience:

template<class T> using min_heap = priority_queue<T, std::vector<T>, std::greater<T>>;

And use it like this:

min_heap<int> my_heap;

Answer 2

Multiply values with -1 and use max heap to get the effect of min heap

Answer 3

Based on above all answers I created an example code for how to create priority queue. Note: It works C++11 and above compilers

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

using namespace std;

// template for prirority Q
template<class T> using min_heap = priority_queue<T, std::vector<T>, std::greater<T>>;
template<class T> using max_heap = priority_queue<T, std::vector<T>>;

const int RANGE = 1000;

vector<int> get_sample_data(int size);

int main(){
  int n;
  cout << "Enter number of elements N = " ; cin >> n;
  vector<int> dataset = get_sample_data(n);

  max_heap<int> max_pq;
  min_heap<int> min_pq;

  // Push data to Priority Queue
  for(int i: dataset){
    max_pq.push(i);
    min_pq.push(i);
  }

  while(!max_pq.empty() && !min_pq.empty()){
    cout << setw(10) << min_pq.top()<< " | " << max_pq.top() << endl;
    min_pq.pop();
    max_pq.pop();
  }

}


vector<int> get_sample_data(int size){
  srand(time(NULL));
  vector<int> dataset;
  for(int i=0; i<size; i++){
    dataset.push_back(rand()%RANGE);
  }
  return dataset;
}

Output of Above code

Enter number of elements N = 4

        33 | 535
        49 | 411
       411 | 49
       535 | 33