Insertion at the beginning of the Singly linked lists

By now you must be well versed with the concept of Linked list. We learned how to make a linked list and traverse it. In this article we will see how you can insert a node at the beginning of a linked list.

Approach:

1. Declare a head pointer and make it as NULL.

2. Create a new node with data.

3. Make the new node points to the head node.

4. Finally, make the new node as the head node.

Example:

Suppose that the linked list has elements, 10->15->20->NULL.
Now, if we insert 5 at beginning of a linked list, it will look like,
5->15->20->NULL.

Code:

#include<bits/stdc++.h>
using namespace std;

class Node{
    public:
    int data;
    Node *next;
    Node()
    {
        this->next = NULL;
    }
};

void traverseLinkedList(Node *node)
{
    while(node!=NULL)
    {
        cout<<node->data<<", ";
        node = node->next;
    }
}

void insertAtBeginning(int data, Node * &head)
{
    Node *newNode = new Node();
    newNode->data = data;

    newNode->next = head;
    head= newNode;
}

int main()
{
    Node *head = new Node();
    head->data = 10;

    Node *first = new Node();
    first->data = 15;

    Node *last = new Node();
    last->data = 20;

    head->next = first;
    first->next = last;

    cout<<"Before Insertion: ";
    traverseLinkedList(head);

    insertAtBeginning(5, head);

    cout<<"\nAfter Insertion: ";
    traverseLinkedList(head);

    return 0;
}

Output:

Before Insertion: 10, 15, 20, 
After Insertion: 5, 10, 15, 20,

This is how to insert a node at beginning of a singly linked list.