programming-examples/java/Data_Structures/Java Program to Implement Doubly Linked List.java

/*This is a Java Program to implement a Doubly Linked List. A linked list is a data structure consisting of a group of nodes which together represent a sequence. Under the simplest form, each node is composed of a data and a reference (in other words, a link) to the next node in the sequence. This structure allows for efficient insertion or removal of elements from any position in the sequence. In a doubly linked list each node has two links one pointing to the next node in the list and one pointing to the previous node in the list .*/

/*
 *  Java Program to Implement Doubly Linked List
 */

import java.util.Scanner;

/*  Class Node  */
class Node
{
    protected int data;
    protected Node next, prev;

    /* Constructor */
    public Node()
    {
        next = null;
        prev = null;
        data = 0;
    }
    /* Constructor */
    public Node(int d, Node n, Node p)
    {
        data = d;
        next = n;
        prev = p;
    }
    /* Function to set link to next node */
    public void setLinkNext(Node n)
    {
        next = n;
    }
    /* Function to set link to previous node */
    public void setLinkPrev(Node p)
    {
        prev = p;
    }
    /* Funtion to get link to next node */
    public Node getLinkNext()
    {
        return next;
    }
    /* Function to get link to previous node */
    public Node getLinkPrev()
    {
        return prev;
    }
    /* Function to set data to node */
    public void setData(int d)
    {
        data = d;
    }
    /* Function to get data from node */
    public int getData()
    {
        return data;
    }
}

/* Class linkedList */
class linkedList
{
    protected Node start;
    protected Node end ;
    public int size;

    /* Constructor */
    public linkedList()
    {
        start = null;
        end = null;
        size = 0;
    }
    /* Function to check if list is empty */
    public boolean isEmpty()
    {
        return start == null;
    }
    /* Function to get size of list */
    public int getSize()
    {
        return size;
    }
    /* Function to insert element at begining */
    public void insertAtStart(int val)
    {
        Node nptr = new Node(val, null, null);
        if(start == null)
            {
                start = nptr;
                end = start;
            }
        else
            {
                start.setLinkPrev(nptr);
                nptr.setLinkNext(start);
                start = nptr;
            }
        size++;
    }
    /* Function to insert element at end */
    public void insertAtEnd(int val)
    {
        Node nptr = new Node(val, null, null);
        if(start == null)
            {
                start = nptr;
                end = start;
            }
        else
            {
                nptr.setLinkPrev(end);
                end.setLinkNext(nptr);
                end = nptr;
            }
        size++;
    }
    /* Function to insert element at position */
    public void insertAtPos(int val, int pos)
    {
        Node nptr = new Node(val, null, null);
        if (pos == 1)
            {
                insertAtStart(val);
                return;
            }
        Node ptr = start;
        for (int i = 2; i <= size; i++)
            {
                if (i == pos)
                    {
                        Node tmp = ptr.getLinkNext();
                        ptr.setLinkNext(nptr);
                        nptr.setLinkPrev(ptr);
                        nptr.setLinkNext(tmp);
                        tmp.setLinkPrev(nptr);
                    }
                ptr = ptr.getLinkNext();
            }
        size++ ;
    }
    /* Function to delete node at position */
    public void deleteAtPos(int pos)
    {
        if (pos == 1)
            {
                if (size == 1)
                    {
                        start = null;
                        end = null;
                        size = 0;
                        return;
                    }
                start = start.getLinkNext();
                start.setLinkPrev(null);
                size--;
                return ;
            }
        if (pos == size)
            {
                end = end.getLinkPrev();
                end.setLinkNext(null);
                size-- ;
            }
        Node ptr = start.getLinkNext();
        for (int i = 2; i <= size; i++)
            {
                if (i == pos)
                    {
                        Node p = ptr.getLinkPrev();
                        Node n = ptr.getLinkNext();
                        p.setLinkNext(n);
                        n.setLinkPrev(p);
                        size-- ;
                        return;
                    }
                ptr = ptr.getLinkNext();
            }
    }
    /* Function to display status of list */
    public void display()
    {
        System.out.print("\nDoubly Linked List = ");
        if (size == 0)
            {
                System.out.print("empty\n");
                return;
            }
        if (start.getLinkNext() == null)
            {
                System.out.println(start.getData() );
                return;
            }
        Node ptr = start;
        System.out.print(start.getData()+ " <-> ");
        ptr = start.getLinkNext();
        while (ptr.getLinkNext() != null)
            {
                System.out.print(ptr.getData()+ " <-> ");
                ptr = ptr.getLinkNext();
            }
        System.out.print(ptr.getData()+ "\n");
    }
}

/* Class DoublyLinkedList */
public class DoublyLinkedList
{
    public static void main(String[] args)
    {
        Scanner scan = new Scanner(System.in);
        /* Creating object of linkedList */
        linkedList list = new linkedList();
        System.out.println("Doubly Linked List Test\n");
        char ch;
        /*  Perform list operations  */
        do
            {
                System.out.println("\nDoubly Linked List Operations\n");
                System.out.println("1. insert at begining");
                System.out.println("2. insert at end");
                System.out.println("3. insert at position");
                System.out.println("4. delete at position");
                System.out.println("5. check empty");
                System.out.println("6. get size");
                int choice = scan.nextInt();
                switch (choice)
                    {
                    case 1 :
                        System.out.println("Enter integer element to insert");
                        list.insertAtStart( scan.nextInt() );
                        break;
                    case 2 :
                        System.out.println("Enter integer element to insert");
                        list.insertAtEnd( scan.nextInt() );
                        break;
                    case 3 :
                        System.out.println("Enter integer element to insert");
                        int num = scan.nextInt() ;
                        System.out.println("Enter position");
                        int pos = scan.nextInt() ;
                        if (pos < 1 || pos > list.getSize() )
                            System.out.println("Invalid position\n");
                        else
                            list.insertAtPos(num, pos);
                        break;
                    case 4 :
                        System.out.println("Enter position");
                        int p = scan.nextInt() ;
                        if (p < 1 || p > list.getSize() )
                            System.out.println("Invalid position\n");
                        else
                            list.deleteAtPos(p);
                        break;
                    case 5 :
                        System.out.println("Empty status = "+ list.isEmpty());
                        break;
                    case 6 :
                        System.out.println("Size = "+ list.getSize() +" \n");
                        break;
                    default :
                        System.out.println("Wrong Entry \n ");
                        break;
                    }
                /*  Display List  */
                list.display();
                System.out.println("\nDo you want to continue (Type y or n) \n");
                ch = scan.next().charAt(0);
            }
        while (ch == 'Y'|| ch == 'y');
    }
}

/*Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
1
Enter integer element to insert
5

Doubly Linked List = 5

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
1
Enter integer element to insert
2

Doubly Linked List = 2 <-> 5

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
2
Enter integer element to insert
6

Doubly Linked List = 2 <-> 5 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
1
Enter integer element to insert
7

Doubly Linked List = 7 <-> 2 <-> 5 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
3
Enter integer element to insert
3
Enter position
3

Doubly Linked List = 7 <-> 2 <-> 3 <-> 5 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
4
Enter position
2

Doubly Linked List = 7 <-> 3 <-> 5 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
3
Enter integer element to insert
4
Enter position
4

Doubly Linked List = 7 <-> 3 <-> 5 <-> 4 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
6
Size = 5


Doubly Linked List = 7 <-> 3 <-> 5 <-> 4 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
4
Enter position
1

Doubly Linked List = 3 <-> 5 <-> 4 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
4
Enter position
2

Doubly Linked List = 3 <-> 4 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
4
Enter position
2

Doubly Linked List = 3 <-> 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
4
Enter position
1

Doubly Linked List = 6

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
4
Enter position
1

Doubly Linked List = empty

Do you want to continue (Type y or n)

y

Doubly Linked List Operations

1. insert at begining
2. insert at end
3. insert at position
4. delete at position
5. check empty
6. get size
5
Empty status = true

Doubly Linked List = empty

Do you want to continue (Type y or n)

n