graph adjacency list 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: adjacency list representation of graph

//adjacency list implementation;addedge,check if edge exist,delete an edge,display
/*            0----->1--------
              |        |     |-->4
              |->2---->|->3---
*/
   
#include <iostream>

using namespace std;
#define v 5
class node
{
public:
    int data;
    node*next;
};
node*adjlist[v];
void init()
{
    for(int i=0;i<v;i++)
    {
        adjlist[i]=NULL;
    }
}
void addedge(int str,int en)
{
    node*temp=new node;
    temp->data=en;
    temp->next=adjlist[str];
    adjlist[str]=temp;
}
void hasedge(int str,int en)
{
    node*temp=new node;
    temp=adjlist[str];
    while(temp!=NULL)
    {
        if(temp->data==en)
        {
            cout<<"yes:";
        }
        temp=temp->next;
    }

}
void remove(int str,int en)
{
    if(adjlist[str]==NULL)
    {
        return;
    }

    if(adjlist[str]->data==en)
    {
        node*temp=new node;
        temp=adjlist[str];
        adjlist[str]=adjlist[str]->next;
        delete temp;
    }
    else
    {
        node *ptr=new node;
        ptr=adjlist[str];
        while(ptr->next!=NULL)
        {
            node*temp=new node;
            if(ptr->next->data==en)
            {

                temp=ptr->next;
                ptr->next=ptr->next->next;
                delete temp;
                break;
            }
            ptr=ptr->next;
        }
    }
}
void display()
{
    for(int i=0;i<v;i++)
    {
        node*temp=new node;
        cout<<"adjlist[]"<<i<<endl;
        temp=adjlist[i];
        while(temp!=NULL)
        {
            cout<<temp->data<<" ";
            temp=temp->next;
        }
        cout<<endl;
    }
}

int main()
{
    init();
    addedge(0,1);
    addedge(0,2);
    addedge(0,3);
    addedge(1,3);
    addedge(1,4);
    addedge(2,3);
    addedge(3,4);
    display();
    hasedge(0,3);
    hasedge(0,4);
    remove(0,1);
    remove(1,4);
    display();
    return 0;
}