Java Program For Deleting A Given Node In Linked List Under Given Constraints

Last Updated : 22 Jun, 2022

Given a Singly Linked List, write a function to delete a given node. Your function must follow the following constraints:

It must accept a pointer to the start node as the first parameter and node to be deleted as the second parameter i.e., a pointer to the head node is not global.
It should not return a pointer to the head node.
It should not accept pointer to pointer to the head node.

You may assume that the Linked List never becomes empty.
Let the function name be deleteNode(). In a straightforward implementation, the function needs to modify the head pointer when the node to be deleted is the first node. As discussed in previous post, when a function modifies the head pointer, the function must use one of the given approaches, we can't use any of those approaches here.
Solution:
We explicitly handle the case when the node to be deleted is the first node, we copy the data of the next node to head and delete the next node. The cases when a deleted node is not the head node can be handled normally by finding the previous node and changing the next of the previous node. The following are the implementation.

Java

// Java program to delete a given node 
// in linked list under given constraints
class LinkedList 
{
    static Node head;

    static class Node 
    {
        int data;
        Node next;

        Node(int d) 
        {
            data = d;
            next = null;
        }
    }

    void deleteNode(Node node, Node n) 
    {        
        // When node to be deleted is 
        // head node
        if (node == n) 
        {
            if (node.next == null) 
            {
                System.out.println("There is only one node. The list " + 
                                   "can't be made empty ");
                return;
            }

            // Copy the data of next node to head 
            node.data = node.next.data;

            // Store address of next node
            n = node.next;

            // Remove the link of next node
            node.next = node.next.next;

            // Free memory
            System.gc();

            return;
        }

        // When not first node, follow the normal 
        // deletion process find the previous node
        Node prev = node;
        while (prev.next != null && 
               prev.next != n) 
        {
            prev = prev.next;
        }

        // Check if node really exists in 
        // Linked List
        if (prev.next == null) {
            System.out.println("Given node is not present in Linked List");
            return;
        }

        // Remove node from Linked List
        prev.next = prev.next.next;

        // Free memory
        System.gc();

        return;
    }

    /* Utility function to print a linked list */
    void printList(Node head) {
        while (head != null) {
            System.out.print(head.data + " ");
            head = head.next;
        }
        System.out.println("");
    }

    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.head = new Node(12);
        list.head.next = new Node(15);
        list.head.next.next = new Node(10);
        list.head.next.next.next = new Node(11);
        list.head.next.next.next.next = new Node(5);
        list.head.next.next.next.next.next = new Node(6);
        list.head.next.next.next.next.next.next = new Node(2);
        list.head.next.next.next.next.next.next.next = new Node(3);

        System.out.println("Given Linked List :");
        list.printList(head);
        System.out.println("");
        
        // Let us delete the node with value 10
        System.out.println("Deleting node :" + head.next.next.data);
        list.deleteNode(head, head.next.next);

        System.out.println("Modified Linked list :");
        list.printList(head);
        System.out.println("");

        // Lets delete the first node
        System.out.println("Deleting first Node");
        list.deleteNode(head, head);
        System.out.println("Modified Linked List");
        list.printList(head);

    }
}

// this code has been contributed by Mayank Jaiswal

Output:

Given Linked List: 12 15 10 11 5 6 2 3

Deleting node 10:
Modified Linked List: 12 15 11 5 6 2 3

Deleting first node
Modified Linked List: 15 11 5 6 2 3

Time Complexity: O(n), where n represents the size of the given array.
Auxiliary Space: O(1), no extra space is required, so it is a constant.

Please refer complete article on Delete a given node in Linked List under given constraints for more details!