如何告诉std :: priority_queue刷新它的排序？

问题描述

我有一个指向结构的指针的优先级队列，例如。市。我编辑优先级队列之外的指针，并希望根据新的值告诉优先级队列重新排序自己。

I have a priority queue of pointers to a struct, e.g. city. I edit the pointers outside the priority queue, and want to tell the priority queue to "reorder" itself according to the new values.

我该怎么办？

例如

#include <iostream>
#include <queue>

using namespace std;

struct city {
    int data;
    city *previous;
};

struct Compare {
    bool operator() ( city *lhs, city *rhs )
    {
        return ( ( lhs -> data ) >= ( rhs -> data ) );
    }
};

typedef priority_queue< city *, vector< city * >, Compare > pqueue;

int main()
{
    pqueue cities;

    city *city1 = new city;
    city1 -> data = 5;
    city1 -> previous = NULL;
    cities.push( city1 );

    city *city2 = new city;
    city2 -> data = 3;
    city2 -> previous = NULL;
    cities.push( city2 );

    city1 -> data = 2;
    // Now how do I tell my priority_queue to reorder itself so that city1 is at the top now?

    cout << ( cities.top() -> data ) << "\n";
    // 3 is printed :(

    return 0;
}

b $ b

谢谢。

Thanks.

推荐答案

这是一个有点黑，但没有违法，完成。

This is a bit hackish, but nothing illegal about it, and it gets the job done.

std::make_heap(const_cast<city**>(&cities.top()),
               const_cast<city**>(&cities.top()) + cities.size(),
               Compare());

更新：

如果出现以下情况，请勿使用此黑客：

Do not use this hack if:

• 底层容器不是向量。


• 比较函子的行为会导致您的外部副本与比较 > priority_queue 。


• 您不完全明白这些警告的含义。

• The underlying container is not vector.
• The Compare functor has behavior that would cause your external copy to order differently than the copy of Compare stored inside the priority_queue.
• You don't fully understand what these warnings mean.

你总是可以编写自己的包装堆算法的容器适配器。 priority_queue 只是一个简单的包装器 make / push / pop_heap 。

You can always write your own container adaptor which wraps the heap algorithms. priority_queue is nothing but a simple wrapper around make/push/pop_heap.

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