How can I implement a custom comparator for a priority queue in C++11?

How can I implement a custom comparator for a priority queue in C++11?

You can create a custom comparator by defining a struct or a lambda function that implements the comparison logic.

Can you show me an example using a struct?

Sure! Here's a simple example:

#include <queue>
#include <vector>

struct CustomComparator {
    bool operator()(const int& a, const int& b) {
        return a > b; // Min-heap
    }
};

int main() {
    std::priority_queue<int, std::vector<int>, CustomComparator> pq;
    pq.push(5);
    pq.push(1);
    pq.push(3);
    // Now the top of the queue will be 1
}

What if I want a max-heap instead?

For a max-heap, you can simply change the comparison in the comparator to return a < b;. This will ensure that the largest element is at the top.

Thanks! Can I use a lambda function instead of a struct?

Absolutely! You can define a priority queue with a lambda like this:

auto cmp = [](int left, int right) { return left > right; };
std::priority_queue<int, std::vector<int>, decltype(cmp)> pq(cmp);