Java program to delete a new node from the middle of the doubly linked list

In this program, we will create a doubly linked list and delete a node from the middle of the list. If the list is empty, display the message "List is empty". If the list is not empty, we will calculate the size of the list and then divide it by 2 to get the mid-point of the list. Current will point to head node. We will iterate through the list till mid?point is reached. Now current will point to the middle node. We delete middle node such that current's previous node will point to the current's next node.

Consider the above example, mid-point of above list is 3. Iterate current from head to mid-point. Now, the current is pointing to mid node which needs to be deleted. In this case, node new is the middle node which needs to be deleted. New can be deleted by making node 2 (current's previous node) to point to node 3 (current's next node). Set current to null.

Algorithm

Define a Node class which represents a node in the list. It will have three properties: data, previous which will point to the previous node and next which will point to the next node.
Define another class for creating the doubly linked list, and it has two nodes: head and tail. Initially, head and tail will point to null.
deleteFromMid() will delete a node from the middle of the list:
- It first checks whether the head is null (empty list) then, it will return from the function as there is no node present in the list.
- If the list is not empty, it will check whether the list has only one node.
- If the list has more than one node then, it will calculate the size of the list. Divide the size by 2 and store it in variable mid.
- Iterate through the list till current points to mid node of the list.
- Connect current's previous node to current?s next node.
- Delete the current node by setting it to null.

a. display() will show all the nodes present in the list.

Define a new node 'current' that will point to the head.
Print current.data till current points to null.
Current will point to the next node in the list in each iteration.

Program:

class DeleteMid {

    //Represent a node of the doubly linked list

    class Node{
        int data;
        Node previous;
        Node next;

        public Node(int data) {
            this.data = data;
        }
    }

    public int size = 0;
    //Represent the head and tail of the doubly linked list
    Node head, tail = null;

    //addNode() will add a node to the list
    public void addNode(int data) {
        //Create a new node
        Node newNode = new Node(data);

        //If list is empty
        if(head == null) {
            //Both head and tail will point to newNode
            head = tail = newNode;
            //head's previous will point to null
            head.previous = null;
            //tail's next will point to null, as it is the last node of the list
            tail.next = null;
        }
        else {
            //newNode will be added after tail such that tail's next will point to newNode
            tail.next = newNode;
            //newNode's previous will point to tail
            newNode.previous = tail;
            //newNode will become new tail
            tail = newNode;
            //As it is last node, tail's next will point to null
            tail.next = null;
        }
        //Size will count the number of nodes present in the list
        size++;
    }

    //deleteFromMid() will delete a node from middle of the list
    public void deleteFromMid() {
        //Checks whether list is empty
        if(head == null) {
            return;
        }
        else {
            //current will point to head
            Node current = head;

            //Store the mid position of the list
            int mid = (size % 2 == 0) ? (size/2) : ((size+1)/2);

            //Iterate through list till current points to mid position
            for(int i = 1; i < mid; i++){
                current = current.next;
            }

            //If middle node is head of the list
            if(current == head) {
                head = current.next;
            }
            //If middle node is tail of the list
            else if(current == tail) {
                tail = tail.previous;
            }
            else {
                current.previous.next = current.next;
                current.next.previous = current.previous;
            }
            //Delete the middle node
            current = null;
        }
        size--;
    }

    //display() will print out the nodes of the list
    public void display() {
        //Node current will point to head
        Node current = head;
        if(head == null) {
            System.out.println("List is empty");
            return;
        }
        while(current != null) {
            //Prints each node by incrementing the pointer.

            System.out.print(current.data + " ");
            current = current.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {

        DeleteMid dList = new DeleteMid();
        //Add nodes to the list
        dList.addNode(1);
        dList.addNode(2);
        dList.addNode(3);
        dList.addNode(4);
        dList.addNode(5);

        //Printing original list
        System.out.println("Original List: ");
        dList.display();
        while(dList.head != null) {
            dList.deleteFromMid();
            //Printing updated list
            System.out.println("Updated List: ");
            dList.display();
        }
    }
}

Output:

Original List: 
1 2 3 4 5 
Updated List: 
1 2 4 5 
Updated List: 
1 4 5 
Updated List: 
1 5 
Updated List: 
5 
Updated List: 
List is empty

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