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- // geekforgeeks
- // Program to find Dijkstra's shortest path using
- // priority_queue in STL
- #include<bits/stdc++.h>
- using namespace std;
- # define INF 0x3f3f3f3f
- // iPair ==> Integer Pair
- typedef pair<int, int> iPair;
- // This class represents a directed graph using
- // adjacency list representation
- class Graph
- {
- int V; // No. of vertices
- // In a weighted graph, we need to store vertex
- // and weight pair for every edge
- list< pair<int, int> > *adj;
- public:
- Graph(int V); // Constructor
- // function to add an edge to graph
- void addEdge(int u, int v, int w);
- // prints shortest path from s
- void shortestPath(int s);
- };
- // Allocates memory for adjacency list
- 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)
- {
- // Create a priority queue to store vertices that
- // are being preprocessed. This is weird syntax in C++.
- // Refer below link for details of this syntax
- // https://www.geeksforgeeks.org/implement-min-heap-using-stl/
- priority_queue< iPair, vector <iPair> , greater<iPair> > pq;
- // Create a vector for distances and initialize all
- // distances as infinite (INF)
- vector<int> dist(V, INF);
- // Insert source itself in priority queue and initialize
- // its distance as 0.
- pq.push(make_pair(0, src));
- dist[src] = 0;
- /* Looping till priority queue becomes empty (or all
- distances are not finalized) */
- while (!pq.empty())
- {
- // The first vertex in pair is the minimum distance
- // vertex, extract it from priority queue.
- // vertex label is stored in second of pair (it
- // has to be done this way to keep the vertices
- // sorted distance (distance must be first item
- // in pair)
- int u = pq.top().second;
- pq.pop();
- // 'i' is used to get all adjacent vertices of a vertex
- list< pair<int, int> >::iterator i;
- for (i = adj[u].begin(); i != adj[u].end(); ++i)
- {
- // Get vertex label and weight of current adjacent
- // of u.
- int v = (*i).first;
- int weight = (*i).second;
- // If there is shorted path to v through u.
- if (dist[v] > dist[u] + weight)
- {
- // Updating distance of v
- dist[v] = dist[u] + weight;
- pq.push(make_pair(dist[v], v));
- }
- }
- }
- // Print shortest distances stored in dist[]
- printf("Vertex Distance from Source\n");
- for (int i = 0; i < V; ++i)
- printf("%d \t\t %d\n", i, dist[i]);
- }
- // Driver program to test methods of graph class
- int main()
- {
- // create the graph given in above fugure
- int V = 9;
- Graph g(V);
- // making above shown graph
- 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;
- }
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