DisplayDijkstraPaths.cpp

#include <iostream>
#include <queue>
#include <functional>
#include <list>
using namespace std;
# define INF 0x3f3f3f3f 

typedef pair<int, int> iPair;

class Graph
{
	int V;
	int* p;
	list< pair<int, int> > *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];
	p = new int[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));
}
void PathDisplay(int* p, int i) 
{
	if (p[i] != -1) {
    		PathDisplay(p, p[i]); 
    		cout << i << "  ";
	}
}
void Graph::shortestPath(int src)
{
	priority_queue< iPair, vector <iPair>, greater<iPair> > pq;

	vector<int> dist(V, INF);
	
	for(int i = 0; i < V; i++) {
		p[i] = 0;
	}

	pq.push(make_pair(0, src));
	dist[src] = 0;
	p[src] = -1;

	while (!pq.empty())
	{
		int u = pq.top().second;
		pq.pop();

		list< pair<int, int> >::iterator i;
		for (i = adj[u].begin(); i != adj[u].end(); ++i)
		{
			int v = (*i).first;
			int weight = (*i).second;
			
			//  relaxation
			if (dist[v] > dist[u] + weight)
			{
				dist[v] = dist[u] + weight;
				p[v] = u;
				pq.push(make_pair(dist[v], v));
			}
		}
	}

	cout << "Display Paths:" << endl;
	for (int i = 1; i < V; ++i) {
		cout << i << " -> " << src << "  ";
		PathDisplay(p, i);
		cout << endl;
	}
}

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;
}