Dijkstra Algorithm C Priority Queue

I let n be the maximal number of elements ever stored in the queue.

Dijkstra algorithm c priority queue. You forgot to check if it has already been. Do current queue top. It finds a shortest path tree for a weighted undirected graph. Function dijkstra g s for each vertex v in g distance v infinite previous v null if v s add v to priority queue q distance s 0 while q is not empty u extract min from q for each unvisited neighbour v of u tempdistance distance u edge weight u v if tempdistance distance v distance v tempdistance previous v u return distance previous.

The algorithm can start with a priority queue that contains only one item and insert new items as they are discovered instead of doing a decrease key check whether the key is in the queue. The ordered list you have. Take the origin vertex set the weight of the shortest path to 0 and push it onto the priority queue. Priority queues priority queues can be implemented in a number of ways.

Normally for dijkstra there are two structures. Include include include include limit of unsigned int define infinity 65535 struct nodedistance int node. Foreach edge e v u in g where u has augmented labels w u p u. This is however not necessary.

To resolve this problem do not update a key but insert one more copy of it. In common presentations of dijkstra s algorithm initially all nodes are entered into the priority queue. While the priority queue is not empty pop an entry v w v p v where v is the vertex w v and p v are the augmented labels of v. In this article we will implement djkstra s shortest path algorithm spt using adjacency list and priority queue.

Dijkstra s algorithm for adjacency list representation in c with time complexity o elogv the second implementation is time complexity wise better but is really complex as we have implemented our own priority queue. Stl provides priority queue but the provided priority queue doesn t support decrease key and delete operations. Priority queues and dijkstra s algorithm slide 5 46. This is the basis on which the elements of a priority queue are sorted and kept in the queue here the criteria is that the node with smaller distance should come above the one with larger distance class comparedist public.

You seem to be missing the second i suppose it is stored as part of your graph model. For dijkstra s algorithm it is always recommended to use heap or priority queue as the required operations extract minimum and decrease key match with speciality of heap or priority queue. However the problem is priority queue doesn t support decrease key. Dijkstra algorithm is a greedy algorithm.

If it is decrease its key otherwise insert it.