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Graph implementation using STL for competitive programming | Set 2 (Weighted graph)

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  • Difficulty Level : Easy
  • Last Updated : 16 Jul, 2022
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In Set 1, unweighted graph is discussed. In this post, weighted graph representation using STL is discussed. The implementation is for adjacency list representation of weighted graph. 

Undirected Weighted Graph

We use two STL containers to represent graph: 

  • vector : A sequence container. Here we use it to store adjacency lists of all vertices. We use vertex number as index in this vector.
  • pair : A simple container to store pair of elements. Here we use it to store adjacent vertex number and weight of edge connecting to the adjacent.

The idea is to use a vector of pair vectors. Below code implements the same.

C++




// C++ program to represent undirected and weighted graph
// using STL. The program basically prints adjacency list
// representation of graph
#include <bits/stdc++.h>
using namespace std;
 
// To add an edge
void addEdge(vector <pair<int, int> > adj[], int u,
                                     int v, int wt)
{
    adj[u].push_back(make_pair(v, wt));
    adj[v].push_back(make_pair(u, wt));
}
 
// Print adjacency list representation of graph
void printGraph(vector<pair<int,int> > adj[], int V)
{
    int v, w;
    for (int u = 0; u < V; u++)
    {
        cout << "Node " << u << " makes an edge with \n";
        for (auto it = adj[u].begin(); it!=adj[u].end(); it++)
        {
            v = it->first;
            w = it->second;
            cout << "\tNode " << v << " with edge weight ="
                 << w << "\n";
        }
        cout << "\n";
    }
}
 
// Driver code
int main()
{
    int V = 5;
    vector<pair<int, int> > adj[V];
    addEdge(adj, 0, 1, 10);
    addEdge(adj, 0, 4, 20);
    addEdge(adj, 1, 2, 30);
    addEdge(adj, 1, 3, 40);
    addEdge(adj, 1, 4, 50);
    addEdge(adj, 2, 3, 60);
    addEdge(adj, 3, 4, 70);
    printGraph(adj, V);
    return 0;
}


Python3




# Python3 program to represent undirected
# and weighted graph. The program basically
# prints adjacency list representation of graph
 
# To add an edge
def addEdge(adj, u, v, wt):
     
    adj[u].append([v, wt])
    adj[v].append([u, wt])
    return adj
 
# Print adjacency list representation of graph
def printGraph(adj, V):
     
    v, w = 0, 0
    for u in range(V):
        print("Node", u, "makes an edge with")
 
        for it in adj[u]:
            v = it[0]
            w = it[1]
            print("\tNode", v, "with edge weight =", w)
             
        print()
 
# Driver code
if __name__ == '__main__':
     
    V = 5
    adj = [[] for i in range(V)]
 
    adj = addEdge(adj, 0, 1, 10)
    adj = addEdge(adj, 0, 4, 20)
    adj = addEdge(adj, 1, 2, 30)
    adj = addEdge(adj, 1, 3, 40)
    adj = addEdge(adj, 1, 4, 50)
    adj = addEdge(adj, 2, 3, 60)
    adj = addEdge(adj, 3, 4, 70)
 
    printGraph(adj, V)
 
# This code is contributed by mohit kumar 29


Javascript




<script>
// Javascript program to represent undirected and weighted graph
// using STL. The program basically prints adjacency list
// representation of graph
 
    // To add an edge
    function addEdge(adj,u,v,wt)
    {
        adj[u].push([v,wt]);
        adj[v].push([u,wt]);
        return adj;
       
    }
     
    //Print adjacency list representation of graph
    function printGraph(adj, V)
    {
        let v=0,w=0;
        for(let u=0;u<V;u++)
        {
            document.write("Node "+u+ " makes an edge with<br>");
            for(let it=0;it<adj[u].length;it++)
            {
                v=adj[u][it][0];
                w=adj[u][it][1];
                document.write("        Node "+ v+ " with edge weight ="+ w+"<br>")
            }
        }
    }
     
     
    // Driver code
    let V = 5;
     
    // The below line may not work on all
    // compilers.  If it does not work on
    // your compiler, please replace it with
    // following
    // vector<int> *adj = new vector<int>[V];
    let adj=new Array(V);
    for(let i=0;i<V;i++)
    {
        adj[i]=[];
    }
     
    // Vertex numbers should be from 0 to 4.
    adj = addEdge(adj, 0, 1, 10)
    adj = addEdge(adj, 0, 4, 20)
    adj = addEdge(adj, 1, 2, 30)
    adj = addEdge(adj, 1, 3, 40)
    adj = addEdge(adj, 1, 4, 50)
    adj = addEdge(adj, 2, 3, 60)
    adj = addEdge(adj, 3, 4, 70)
    printGraph(adj, V);
     
     
     
    // This code is contributed by unknown2108
</script>


Java




import java.util.*;
 
// Creation of Adjacency List
// The adjacency List consist of an ArrayList within an
// ArrayList. The inner ArrayList holds the HashMap of
// (vertices,weight)
public class Weighted_Graph {
    int v;
    ArrayList<ArrayList<HashMap<Integer, Integer> > > adj;
    Weighted_Graph(int v)
    {
        this.v = v;
        this.adj = new ArrayList<>();
 
        for (int i = 0; i < v; i++) {
            this.adj.add(new ArrayList<>());
        }
    }
    // Function to add an Edge
    void addEdge(int u, int v, int weight)
    {
        this.adj.get(u).add(new HashMap<>());
        this.adj.get(u)
            .get(this.adj.get(u).size() - 1)
            .put(v, weight);
 
        this.adj.get(v).add(new HashMap<>());
        this.adj.get(v)
            .get(this.adj.get(v).size() - 1)
            .put(u, weight);
    }
 
    // Function for printing the whole graph
    // Stream API has been used
    // to easily access the HashMap elements
    // This code may not work in versions
    // prior to java 8
 
    void printGraph()
    {
        for (int i = 0; i < this.v; i++) {
            System.out.println("\nNode " + i
                               + " makes an edge with ");
            for (HashMap<Integer, Integer> j :
                 this.adj.get(i)) {
                j.entrySet().forEach(
                    e
                    -> System.out.println(
                        "\tNode " + e.getKey()
                        + " with edge weight "
                        + e.getValue() + " "));
            }
        }
    }
    // Main method
    public static void main(String[] args)
    {
        int v = 5;
        Weighted_Graph obj = new Weighted_Graph(v);
        obj.addEdge(0, 1, 10);
        obj.addEdge(0, 4, 20);
        obj.addEdge(1, 2, 30);
        obj.addEdge(1, 3, 40);
        obj.addEdge(1, 4, 50);
        obj.addEdge(2, 3, 60);
        obj.addEdge(3, 4, 70);
        obj.printGraph();
    }
}
// This code is submitted by Abhishek_Manna_HETC


Output: 

Node 0 makes an edge with 
    Node 1 with edge weight =10
    Node 4 with edge weight =20

Node 1 makes an edge with 
    Node 0 with edge weight =10
    Node 2 with edge weight =30
    Node 3 with edge weight =40
    Node 4 with edge weight =50

Node 2 makes an edge with 
    Node 1 with edge weight =30
    Node 3 with edge weight =60

Node 3 makes an edge with 
    Node 1 with edge weight =40
    Node 2 with edge weight =60
    Node 4 with edge weight =70

Node 4 makes an edge with 
    Node 0 with edge weight =20
    Node 1 with edge weight =50
    Node 3 with edge weight =70

This article is contributed by Sahil Chhabra. and improved by Kunal Verma If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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