#include <iostream>
#include <cstdlib>
using namespace std;

/*
 * Adjacency List Node
 */
struct AdjListNode
{
    int data;
    struct AdjListNode* next;
};

/*
 * Adjacency List
 */
struct AdjList
{
    struct AdjListNode *head;
};

/*
 * Class Graph
 */
class Graph
{
    private:
        int V;
        AdjList* array;
    public:
        Graph(int V)
        {
            this->V = V;
            array = new AdjList [V];         //total vertices
            for (int i = 0; i < V; ++i)
                array[i].head = NULL;       //linking head of all vertices (array) to NULL ,it doesn't store any number only stores HEAD
        }

        /*
         * Adding Edge to Graph
         */
        void addEdge(int src, int dest)
        {
                                                // 0-->2
                                                // 1-->NULL
                                                // 2-->0

          // Add an edge from src to dest.  A new node is added to the adjacency
        // list of src.  The node is added at the begining

            AdjListNode* newNode = new AdjListNode;  //newNode stores both data(dest) and *next pointer
            newNode->data = dest;                   //consider src = 0 and dest = 1     0<----->1 for undirected graph
            newNode->next = NULL;       //  1----->NULL
                                                    //adding nodes at beginning of each list just like in linked list//
            newNode->next = array[src].head;        //*next(of dst) storing address of head->next node i.e.. 1--->2 (first node from head)
            array[src].head = newNode;              //  0-->1-->2

             // Since graph is undirected, add an edge from dest to src also
            newNode = new AdjListNode;               //now newNode storing data(src)
            newNode->data = src;
            newNode->next = NULL;               // 0--->NULL

            newNode->next = array[dest].head;   // 0---->NULL (bcuz.. 1-->NULL)
            array[dest].head = newNode;         // 1---->0
        }
        /*
         * Print the graph
         */
        void printGraph()
        {
            int v;
            for (v = 0; v < V; ++v)
            {
                AdjListNode* tmp = array[v].head;       //tmp has the address of (0,1..)vertex head
                cout<<"\n Adjacency list of vertex "<<v<<"\n head ";
                while (tmp)
                {
                    cout<<"-> "<<tmp->data;
                    tmp = tmp->next;
                }
                cout<<endl;
            }
        }
};

/*
 * Main
 */
int main()
{
    Graph gh(5);
    gh.addEdge(0, 1);
    gh.addEdge(0, 4);
    gh.addEdge(1, 2);
    gh.addEdge(1, 3);
    gh.addEdge(1, 4);
    gh.addEdge(2, 3);
    gh.addEdge(3, 4);

    // print the adjacency list representation of the above graph
    gh.printGraph();

    return 0;
}