Performance of Dijkstra's algorithm implementation

Question

Below is an implementation of Dijkstra\'s algorithm I wrote from the pseudocode in the Wikipedia article. For a graph with about 40 000 nodes and 80 000 edges, it takes 3 o

Answer 1

Use priority_queue.

My Dijkstra implementation:

struct edge
{
    int v,w;
    edge(int _w,int _v):w(_w),v(_v){}
};
vector > g;
enum color {white,gray,black};
vector dijkstra(int s)
{
    int n=g.size();
    vector d(n,-1);
    vector c(n,white);
    d[s]=0;
    c[s]=gray;
    priority_queue,vector >,greater > > q; // declare priority_queue
    q.push(make_pair(d[s],s)); //push starting vertex
    while(!q.empty())
    {
        int u=q.top().second;q.pop(); //pop vertex from queue
        if(c[u]==black)continue;
        c[u]=black; 
        for(int i=0;id[u]+w) //shorter path to gray vertex found
            {
                d[v]=d[u]+w;
                q.push(make_pair(d[v],v)); //push this vertex to queue
            }
        }
    }
    return d;
}