c++ priority queue list code example

Example 1: priority queue c++

/* A priority queue maintains a set of elements. The supported operations are
insertion and, depending on the type of the queue, retrieval and removal 
of either the minimum or maximum element. Insertion and removal take 
O(logn) time, and retrieval takes O(1) time. */
priority_queue<int> q;
q.push(3); // 3
q.push(5); // 3 5
q.push(7); // 3 5 7
q.push(2); // 2 3 5 7
cout << q.top() << "\n"; // 7
q.pop();
cout << q.top() << "\n"; // 5
q.pop();
q.push(6);
cout << q.top() << "\n"; // 6
q.pop();

Example 2: priority queue cpp

// using GCC 10.2 (C++2a) compiler
#include <functional>
#include <queue>
#include <vector>
#include <iostream>
 
template<typename T> void print_queue(T& q) {
    while(!q.empty()) {
        std::cout << q.top() << " ";
        q.pop();
    }
    std::cout << '\n';
}
 
int main() {
    std::priority_queue<int> q;
 
    for(int n : {1,8,5,6,3,4,0,9,7,2})
        q.push(n);
 
    print_queue(q);
 
    std::priority_queue<int, std::vector<int>, std::greater<int> > q2;
 
    for(int n : {1,8,5,6,3,4,0,9,7,2})
        q2.push(n);
 
    print_queue(q2);
 
    // Using lambda to compare elements.
    auto cmp = [](int left, int right) { return (left ^ 1) < (right ^ 1); };
    std::priority_queue<int, std::vector<int>, decltype(cmp)> q3(cmp);
 
    for(int n : {1,8,5,6,3,4,0,9,7,2})
        q3.push(n);
 
    print_queue(q3);
 
}