prim.cpp

#include<bits/stdc++.h>
using namespace std;
# define INF 0x3f3f3f3f
 

typedef pair<int, int> iPair;
 

class Graph
{
    int V;    
    list<iPair> *adj;
 
public:
    Graph(int V);  
 
    
    void addEdge(int u, int v, int w);
 
    void shortestPath(int s);
};
 
Graph::Graph(int V)
{
    this->V = V;
    adj = new list<iPair> [V];
}
 
void Graph::addEdge(int u, int v, int w)
{
    adj[u].push_back(make_pair(v, w));
    adj[v].push_back(make_pair(u, w));
}
 
// Prints shortest paths from src to all other vertices
void Graph::shortestPath(int src)
{
    
    priority_queue< iPair, vector <iPair> , greater<iPair> > pq;
 
   
    vector<int> dist(V, INF);
    vector<int> parent(V, -1);
    vector<bool> inMST(V, false);
    pq.push(make_pair(0, src));
    dist[src] = 0;
   
    while (!pq.empty())
    {
        
        int u = pq.top().second;
        pq.pop();
        inMST[u] = true;
       
        list< pair<int, int> >::iterator i;
        for (i = adj[u].begin(); i != adj[u].end(); ++i)
        {
            
            int v = (*i).first;
            int weight = (*i).second;
 
           
            if (dist[v] > weight && inMST[v] == false)
            {
                
                dist[v] = weight;
                parent[v] = u;
                pq.push(make_pair(dist[v], v));
            }
        }
    }
 
   
    printf("Vertex Parents from Source\n");
    for (int i = 1; i < V; ++i)
        printf("%d - %d\n",parent[i],i);
}
 

int main()
{
    int V = 9;
    Graph g(V);
 
    
    g.addEdge(0, 1, 4);
    g.addEdge(0, 7, 8);
    g.addEdge(1, 2, 8);
    g.addEdge(1, 7, 11);
    g.addEdge(2, 3, 7);
    g.addEdge(2, 8, 2);
    g.addEdge(2, 5, 4);
    g.addEdge(3, 4, 9);
    g.addEdge(3, 5, 14);
    g.addEdge(4, 5, 10);
    g.addEdge(5, 6, 2);
    g.addEdge(6, 7, 1);
    g.addEdge(6, 8, 6);
    g.addEdge(7, 8, 7);
 
    g.shortestPath(0);
 
    return 0;
}