boost priority queue, see if element is already in the queue

Question

I need the above functionality for pathfinding.

I'm using the boost queue as it apparently allows me to do this.

I have my queue setup like so:

typedef boost::heap::priority_queue<PathFindingNode *, boost::heap::compare<MyClassCompare> > MyPriorityQueue;

I want to create a method that takes in type PathFindingNode as a parameter, then checks to see if this Node is already in the queue.

I found I could iterate through the queue like this:

typename MyPriorityQueue::iterator begin = self.queue->begin();
typename MyPriorityQueue::iterator end = self.queue->end();

for (typename MyPriorityQueue::iterator it = begin; it != end; ++it)
{
}

But I don't understand how to use the it value to compare against a node passed into the method block?

Answer 1

If you iterate over the queue each time, you'll kill the performance guarantees of your algorithm. Instead, you should store the handle returned from the queue upon adding a new entry into the queue and use the handle to potentially update the priority of the entry. You might need to use one of the node-based priority queues, however.

You could e.g. use the Fibonacci Heap whose push() yields a handle_type. You'd store this value with your node and later use with increase() or decrease() to adjust the priority of the node in the heap.