how to make a graph in c++ code example

Example 1: graph c++

//Code by Soumyadeep Ghosh insta- @soumyadepp
//linked in :  https://www.linkedin.com/in/soumyadeep-ghosh-90a1951b6/
//Basic implementation of undirected graph using OOP

#include <bits/stdc++.h>

using namespace std;

//undirected graph
class graph
{
  vector<int>*adjacency_list; //array of vectors to store adjacency list
  int Vertices;
  public:
    //constructor
    graph(int n)
    {
      Vertices=n;
      adjacency_list=new vector<int>[Vertices]; //dynamic allocation
    }
  
    void add_edge(int,int);
    void display_graph();
};

int main()
{
  graph g1(5);  //graph of 5 vertices indices- 0 to 4
  //adding edges
  g1.add_edge(0,1); //connect node number 0 to node number 1
  g1.add_edge(1,2); //connect node number 1 to node number 2
  g1.add_edge(1,3); //connect node number 1 to node number 3
  g1.add_edge(2,4); //connect node number 2 to node number 4
  g1.add_edge(2,3); //connect node number 2 to node number 3
  //displaying the graph
  cout<<"The entered Graph is "<<endl;
  g1.display_graph();
  return 0;
}

//function definitions
void graph::add_edge( int u,int v )
   {
     if( u >= Vertices || v >= Vertices )
     {
       cout<<"Overflow"<<endl;
       return;
     }
     if( u<0 || v<0 )
     {
       cout<<"underflow"<<endl;
       return;
     }
     adjacency_list[u].push_back(v);
     adjacency_list[v].push_back(u);
   }
  void graph::display_graph()
   {
     for(int i=0;i<Vertices;i++)
     {
       cout<<"Adjacency list of vertex of vertex "<<i<<endl;
       for(auto it:adjacency_list[i]) //traverse through each list
       {
         cout<<it<<" ";
       }
       cout<<endl;
     }
   }
//thank you!

Example 2: how to make graphs in c++

#include <iostream>
using namespace std;
// stores adjacency list items
struct adjNode {
    int val, cost;
    adjNode* next;
};
// structure to store edges
struct graphEdge {
    int start_ver, end_ver, weight;
};
class DiaGraph{
    // insert new nodes into adjacency list from given graph
    adjNode* getAdjListNode(int value, int weight, adjNode* head)   {
        adjNode* newNode = new adjNode;
        newNode->val = value;
        newNode->cost = weight;
         
        newNode->next = head;   // point new node to current head
        return newNode;
    }
    int N;  // number of nodes in the graph
public:
    adjNode **head;                //adjacency list as array of pointers
    // Constructor
    DiaGraph(graphEdge edges[], int n, int N)  {
        // allocate new node
        head = new adjNode*[N]();
        this->N = N;
        // initialize head pointer for all vertices
        for (int i = 0; i < N; ++i)
            head[i] = nullptr;
        // construct directed graph by adding edges to it
        for (unsigned i = 0; i < n; i++)  {
            int start_ver = edges[i].start_ver;
            int end_ver = edges[i].end_ver;
            int weight = edges[i].weight;
            // insert in the beginning
            adjNode* newNode = getAdjListNode(end_ver, weight, head[start_ver]);
             
                        // point head pointer to new node
            head[start_ver] = newNode;
             }
    }
      // Destructor
     ~DiaGraph() {
    for (int i = 0; i < N; i++)
        delete[] head[i];
        delete[] head;
     }
};
// print all adjacent vertices of given vertex
void display_AdjList(adjNode* ptr, int i)
{
    while (ptr != nullptr) {
        cout << "(" << i << ", " << ptr->val
            << ", " << ptr->cost << ") ";
        ptr = ptr->next;
    }
    cout << endl;
}
// graph implementation
int main()
{
    // graph edges array.
    graphEdge edges[] = {
        // (x, y, w) -> edge from x to y with weight w
        {0,1,2},{0,2,4},{1,4,3},{2,3,2},{3,1,4},{4,3,3}
    };
    int N = 6;      // Number of vertices in the graph
    // calculate number of edges
    int n = sizeof(edges)/sizeof(edges[0]);
    // construct graph
    DiaGraph diagraph(edges, n, N);
    // print adjacency list representation of graph
    cout<<"Graph adjacency list "<<endl<<"(start_vertex, end_vertex, weight):"<<endl;
    for (int i = 0; i < N; i++)
    {
        // display adjacent vertices of vertex i
        display_AdjList(diagraph.head[i], i);
    }
    return 0;
}