支持修改元素值的优先队列

支持修改元素值的优先[[队列]]

If you want to modify an element in a priority queue, you would need to remove the element, modify it, and then insert it back into the priority queue. However, this can be inefficient for large priority queues since removing and inserting elements can be expensive operations.

In C++, the standard priority queue container does not provide a direct way to modify elements. Instead, you would need to implement a custom priority queue data structure that allows efficient modification of elements.

One way to do this is to use a combination of a heap-based priority queue and a hash table (or a map) that maps elements to their positions in the heap. The hash table allows fast lookup of an element's position in the heap, and the heap-based priority queue allows efficient access to the highest-priority element.

Here is a simple example of a custom priority queue data structure that supports efficient modification of elements:

#include <queue>
#include <unordered_map>

template <typename T>
class CustomPriorityQueue {
public:
    void push(const T& val) {
        pq.push(val);
        pos[val] = pq.size() - 1;
    }

    void pop() {
        pos.erase(pq.top());
        pq.pop();
    }

    void modify(const T& old_val, const T& new_val) {
        auto it = pos.find(old_val);
        if (it == pos.end()) {
            return;
        }

        int i = it->second;
        pq.pop();

        if (i != pq.size()) {
            pq.push(pq.top());
            pos[pq.top()] = i;
            pq.pop();
        }

        pos.erase(it);
        push(new_val);
    }

    const T& top() const {
        return pq.top();
    }

    bool empty() const {
        return pq.empty();
    }

private:
    std::priority_queue<T> pq;
    std::unordered_map<T, int> pos;
};