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Given the task is to count the number of edges in an undirected graph. An undirected graph is a set of vertices which are connected together to form a graph, whose all the edges are bidirectional. Undirected graphs can travel in any direction from one node to another connected node.

Below is a visual representation of the undirected graph.

Now, according to the problem we have to find the number of edges in the undirected graph.

Edges in a graph are the lines to which two vertices are joined.

**Input** −

insert(graph_list, 0, 1); insert(graph_list, 0, 2); insert(graph_list, 1, 2); insert(graph_list, 1, 4); insert(graph_list, 2, 4); insert(graph_list, 2, 3); insert(graph_list, 3, 4);

**Output** −

count of edges are: 7

Initialise a list to store all the vertices of the graph’s list and insert the values accordingly.

In function count_edges, declare a variable count=0 which is to return the count of the edges.

Traverse the list using a loop until we reach the last vertice and add the value of count with graph_list[i].size() and store it back to the count variable.

After we reach the last vertice, divide the value of count by two, and print the result.

#include<bits/stdc++.h> using namespace std; //function to insert vertices void insert(list<int> graph_list[], int u, int v){ graph_list[u].push_back(v); graph_list[v].push_back(u); } //function to count the total number of edges void count_edges(list<int> graph_list[], int v){ int count=0; //traverse the loop till the vertice is found for (int i = 0 ; i < v ; i++){ count += graph_list[i].size(); } count = count/2; cout<<"count of edges are: "<<count; } int main(int argc, char* argv[]){ //creating 5 vertices in a graph int vertices = 5; //declare list to create a graph and pass the vertices list<int> graph_list[vertices]; //call insert function passing the list variable, vertice, linked vertice insert(graph_list, 0, 1); insert(graph_list, 0, 2); insert(graph_list, 1, 2); insert(graph_list, 1, 4); insert(graph_list, 2, 4); insert(graph_list, 2, 3); insert(graph_list, 3, 4); //calling count function that will count the edges count_edges(graph_list, vertices); return 0 ; }

If we run the above code we will get the following output −

count of edges are: 7

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