Linked List: Program to delete a node from linked list

Write a program to delete a node from the linked list

Linked list is a series of nodes in which each node contains a data field and
reference (pointer) to the next node in the list.

There are two cases for deleting a node from a linked list

1. Deleting the node from the start of the linked list

   • For deleting node from the start, we have to simply make head as head.next



2. Deleting the node from the end of linked list

   • To delete node at the end we can refer the following steps
   • Create a pointer 'current' and set on the head
   • While current.next.next is not NULL, make current as current.next
   • After the loop terminates, make current.next as NULL to remove the last node

Complexity

Time Complexity : O(n) , where n is the size of linked list
Space Complexity : O(1)

Java Code

   import java.util.*;
 
    class Node {
        // initialising data field and next pointer of node
        int data;
        Node next;
     
        Node(int d) {
            this.data = d;
            this.next = null;
        }
    }
     
    class LinkedList {
        Node head;
     
        // creating a linked list using array
        public void buildLinkedlist(int A[], int noOfNodes) {
            int i;
            Node temp, last;
            temp = new Node(A[0]);
            temp.next = null;
            head = temp;
            last = temp;
            for (i = 1; i < noOfNodes; i++) {
                temp = new Node(A[i]);
                temp.next = null;
                last.next = temp;
                last = temp;
            }
        }
     
        // printing of linkedList
        public void printLinkedlist() {
            List allNodesList = new ArrayList<>();
            Node temp = head;
            while (temp != null) {
                allNodesList.add(Integer.toString(temp.data));
                temp = temp.next;
            }
            System.out.println(String.join(" -> ", allNodesList));
        }
     
        // deleting node from start
        public void deleteStartNode() {
            Node current = head;
            head = head.next;
            current.next = null;
        }
     
        // deleting node from end
        public void deleteEndNode() {
     
            if (head == null)
                return;
            Node current = head;
            if (current.next == null) {
                head = null;
            }
            while (current.next.next != null) {
                current = current.next;
            }
            current.next = null;
     
        }
     
        public static void main(String[] args) {
            int[] linkedlistElements = new int[] { 10 };
            int numberOfNodes = 1;
            // Initializing object of linkedlist class
            LinkedList ll = new LinkedList();
            ll.buildLinkedlist(linkedlistElements, numberOfNodes);
            System.out.println("Given Linked List ");
            ll.printLinkedlist();
            System.out.println("Linked List after deleting first node");
            ll.deleteStartNode();
            ll.printLinkedlist();
            System.out.println("Linked List after deleting last node");
            ll.deleteEndNode();
            ll.printLinkedlist();
     
        }
    } 

Output

Given Linked List
10 -> 30 -> 50 -> 40 -> 70 -> 90
Linked List after deleting first node
30 -> 50 -> 40 -> 70 -> 90
Linked List after deleting last node
30 -> 50 -> 40 -> 70