Insert node at the beginning of a Singly Linked List
Insertion in a Singly Linked List
When using a singly linked list, we can easily insert an element at the beginning of the list, as shown in Figure below. The main idea is that we create a new node, set its next link to refer to the same object as head, and then set head to point to the new node.
Insert at the beginning:
public void insertFirst(int value) { Node newNode = new Node(value); newNode.next = head; head = newNode; }
Example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | /*Node of a single linked list of integer */ public class SinglyLinkedList { private static Node head; /* instance variable */ private static class Node { private int data; /* we assume data integer */ private Node next; /* Create a node with the given data and next node */ public Node(int data) { this.data = data; this.next = null; } } /* Display single list */ public void display() { Node current = head; while (current != null) { System.out.print(current.data + " --> "); current = current.next; } System.out.println("null"); } public void insertFirst(int value) { Node newNode = new Node(value); newNode.next = head; head = newNode; } public static void main(String[] args) { SinglyLinkedList s = new SinglyLinkedList(); s.head = new Node(10); Node second = new Node(7); Node third = new Node(20); Node fourth = new Node(8); s.head.next = second; // 10 --> 7 second.next = third; // 10 -->7 -->20 third.next = fourth; // 10 -->7 -> 20 -->8 -->null s.display(); System.out.println("Insert at the beginning:"); s.insertFirst(4); s.display(); } } |
Output:
10 --> 7 --> 20 --> 8 --> null Insert at the beginning: 4 --> 10 --> 7 --> 20 --> 8 --> null
