Priority queue in C++ and python

By default, python support min priority queue while C++ supports max priority queue.

C++

Min and Max priority queue implementations in C++

Min Heap and Max Heap Implementation in C++ - Techie Delight

https://stackoverflow.com/questions/2786398/is-there-an-easy-way-to-make-a-min-heap-in-c

#include <queue> // functional,iostream,ctime,cstdlib
using namespace std;

int main(int argc, char* argv[])
{
    srand(time(0));
    priority_queue<int,vector<int>,greater<int> > q;
    for( int i = 0; i != 10; ++i ) q.push(rand()%10);
    cout << "Min-heap, popped one by one: ";
    while( ! q.empty() ) {
        cout << q.top() << ' ';  // 0 3 3 3 4 5 5 6 8 9
        q.pop();
    }
    cout << endl;
    return 0;
}

How to implement Min Heap using STL? - GeeksforGeeks

Max heap

// C++ program to show that priority_queue is by 
// default a Max Heap 
#include <bits/stdc++.h> 
using namespace std;
// Driver code 
int main () 
{ 
 // Creates a max heap 
 priority_queue <int> pq; 
 pq.push(5); 
 pq.push(1); 
 pq.push(10); 
 pq.push(30); 
 pq.push(20);
// One by one extract items from max heap 
 while (pq.empty() == false) 
 { 
  cout << pq.top() << " "; 
  pq.pop(); 
 }
return 0; 
}

Min heap

// C++ program to use priority_queue to implement min heap 
#include <bits/stdc++.h> 
using namespace std;
// Driver code 
int main () 
{ 
 // Creates a min heap 
 priority_queue <int, vector<int>, greater<int> > pq; 
 pq.push(5); 
 pq.push(1); 
 pq.push(10); 
 pq.push(30); 
 pq.push(20);
// One by one extract items from min heap 
 while (pq.empty() == false) 
 { 
  cout << pq.top() << " "; 
  pq.pop(); 
 }
return 0; 
}

Priority Queue in C++ Standard Template Library (STL) - GeeksforGeeks

Note : The above syntax is difficult to remembers, so in case of numeric values, we can multiply values with -1 and use max heap to get the effect of min heap

Python

python is relatively simple. We can use -item to change min priority queue to max priority queue.

import heapq
#min heap
a = [6,1,0,4,5,6]
heapq.heapify(a)
while a:
    print(heapq.heappop(a))
"""
0
1
4
5
6
6
  
"""
#max heap
a = [6,1,0,4,5,6]
a = [-item for item in a]
heapq.heapify(a)
while a:
    print(-heapq.heappop(a))
"""
6
6
5
4
1
0
"""