Custom Comparison Function for Priority Queue

To define a custom comparison function for a priority queue of custom objects, you can create a function object (functor) or use a lambda expression that takes two objects of the custom type and returns a boolean value indicating whether the first object should have a higher priority than the second object.

Here's an example of defining a custom comparison function using a lambda expression for a priority queue of Player objects:

1#include <iostream>
2#include <queue>
3#include <string>
4
5struct Player {
6  std::string name;
7  int score;
8};
9
10int main() {
11  auto cmp = [](const Player& p1,
12    const Player& p2) {
13    return p1.score < p2.score;
14  };
15
16  std::priority_queue<Player,
17    std::vector<Player>, decltype(cmp)> pq(cmp);
18
19  pq.push({"Alice", 100});
20  pq.push({"Bob", 80});
21  pq.push({"Charlie", 120});
22
23  while (!pq.empty()) {
24    std::cout << pq.top().name << ": "
25      << pq.top().score << std::endl;
26    pq.pop();
27  }
28}

In this example, the lambda expression cmp compares two Player objects based on their score member. The player with a higher score will have a higher priority in the queue.

The custom comparison function is passed as the third template argument to the std::priority_queue declaration, and an instance of the comparison function is passed to the constructor of the priority queue.

When you run this code, it will output the players in descending order of their scores:

1Charlie: 120
2Alice: 100
3Bob: 80

By defining a custom comparison function, you can easily customize the priority ordering of objects in a priority queue based on your specific requirements.