Count edges in a graph, C++ (gcc)

Count edges in a graph

#include<bits/stdc++.h> 
using namespace std; 
  
// Adjacency list representation of graph 
class Graph 
{ 
    int V; 
    list<int> *adj; 
    public : 
        Graph(int V) 
        { 
            this->V = V ; 
            adj = new list<int>[V]; 
        } 
        void addEdge(int u, int v); 
        int countEdges(); 
}; 
  
// add edge to graph 
void Graph :: addEdge ( int u, int v ) 
{ 
    adj[u].push_back(v); 
    adj[v].push_back(u); 
} 
  
// Returns count of edge in undirected graph 
int Graph :: countEdges() 
{ 
    int sum = 0; 
  
    //traverse all vertex 
    for (int i = 0 ; i < V ; i++) 
  
        // add all edge that are linked to the 
        // current vertex 
        sum += adj[i].size(); 
  
  
    // The count of edge is always even because in 
    // undirected graph every edge is connected 
    // twice between two vertices 
    return sum/2; 
} 
  
// driver program to check above function 
int main() 
{ 
    int V = 5 ; 
    Graph g(V); 
  
    // making above uhown graph 
    g.addEdge(1,2 ); 
    g.addEdge(1,3 ); 
    g.addEdge(2,3 ); 
    g.addEdge(3,4 ); 
    g.addEdge(2,4 ); 
    
    cout << g.countEdges() << endl; 
  
    return 0; 
}


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