Dijkstra-Algorithm.cpp

Question Implementing Dijkstra Algorithm 
Given a weighted, undirected and connected graph of V vertices and an adjacency list adj where adj[i] is a list of lists containing two integers where the first integer of each list j denotes there is edge between i and j , second integers corresponds to the weight of that  edge . You are given the source vertex S and You to Find the shortest distance of all the vertex's from the source vertex S. You have to return a list of integers denoting shortest distance between each node and Source vertex S.

 

Note: The Graph doesn't contain any negative weight cycle.
Question Link - https://practice.geeksforgeeks.org/problems/implementing-dijkstra-set-1-adjacency-matrix/1
Youtube Link - https://youtu.be/SQ-pXKsBBz8

//{ Driver Code Starts

#include<bits/stdc++.h>

using namespace std;

// } Driver Code Ends

class Solution

{

    public:

    //Function to find the shortest distance of all the vertices

    //from the source vertex S.

    vector <int> dijkstra(int V, vector<vector<int>> adj[], int S)

    {

        // Code here

        priority_queue<pair<int,int>, vector<pair<int, int>>, greater<pair<int,int>>> pq;

        

        vector<int> dist(V);

        for (int i=0; i<V; i++){

            dist[i]=1e9;

        }

        

        dist[S]=0;

        pq.push({0,S});

        

        while (pq.empty()==false){

            int dis=pq.top().first;

            int node=pq.top().second;

            pq.pop();

            

            for (auto it : adj[node]){

                int edgeweight=it[1];

                int adjnode=it[0];

                

                if (dis + edgeweight < dist[adjnode]){

                    dist[adjnode] = dis+ edgeweight;

                    pq.push({dist[adjnode], adjnode});

                }

            }

        }

        return dist;

    }

};

//{ Driver Code Starts.

int main()

{

    int t;

    cin >> t;

    while (t--) {

        int V, E;

        cin >> V >> E;

        vector<vector<int>> adj[V];

        int i=0;

        while (i++<E) {

            int u, v, w;

            cin >> u >> v >> w;

            vector<int> t1,t2;

            t1.push_back(v);

            t1.push_back(w);

            adj[u].push_back(t1);

            t2.push_back(u);

            t2.push_back(w);

            adj[v].push_back(t2);

        }

        int S;

        cin>>S;

        

        Solution obj;

    	vector<int> res = obj.dijkstra(V, adj, S);    	

    	for(int i=0; i<V; i++)

    	    cout<<res[i]<<" ";

    	cout<<endl;

    }

    return 0;

}

// } Driver Code Ends