Question

To class DoublyLinkedList, add method reverse which reverses the order of the elements in the list.

For Java, JavaEclipse. Course Data Structures.

Answer 1

Sample Code of Reverse( ) :

public void reverse() {
// temp is helping variable for swaping
DLL_Node temp = null;
DLL_Node p_crawl = dll_head;
  
// swaping prev and next address of each node
while (p_crawl != null) {
temp = p_crawl.prev;
p_crawl.prev = p_crawl.next;
p_crawl.next = temp;
p_crawl = p_crawl.prev;
}
if (temp != null) {
dll_head = temp.prev;
}
}

Sample Code of running Full Java Program :

import java.lang.*;
import java.util.*;

public class DoublyLinkedList {
class DLL_Node{
int data;
DLL_Node prev; // store address of previous node
DLL_Node next; // store address of next node
  
// contrustor
DLL_Node(int data) {
this.data = data;
}
}
// delaration global variable
DLL_Node dll_head, dll_tail = null;
  
  
public void print_dll() {
DLL_Node p_crawl = dll_head;
if(p_crawl == null) {
return;
}
while(p_crawl != null) {
System.out.print(p_crawl.data + " ");
p_crawl = p_crawl.next;
}
System.out.println();
}
  
// inserting node at end of doublylinkedlist
public void appendDLL_Node(int data) {
DLL_Node dll_node = new DLL_Node(data);
// this condition is true when dll_head nas no node
if(dll_head == null) {
dll_head = dll_tail = dll_node;
dll_head.prev = null;
dll_tail.next = null;
}
else {
dll_tail.next = dll_node;
dll_node.prev = dll_tail;
dll_tail = dll_node;
dll_tail.next = null;
}
}
public void reverse() {
// temp is helping variable for swaping
DLL_Node temp = null;
DLL_Node p_crawl = dll_head;
  
// swaping prev and next address of each node
while (p_crawl != null) {
temp = p_crawl.prev;
p_crawl.prev = p_crawl.next;
p_crawl.next = temp;
p_crawl = p_crawl.prev;
}
if (temp != null) {
dll_head = temp.prev;
}
}
  
  
public static void main(String[] args) {
  
DoublyLinkedList dll = new DoublyLinkedList();
//Adding nodes for creating DoublyLinkedList
for(int i = 1;i<=10;i++)
dll.appendDLL_Node(i*10);
  
// calling function to print elements in doublylinkedlist
// before reverse
System.out.print("nodes before calling reverse function : ");
dll.print_dll();
// calling function to reverse
dll.reverse();
// calling function to print elements in doublylinkedlist
// after reverse
System.out.print("nodes after calling reverse function : ");
dll.print_dll();
  
}
}

Screenshot of Full Java Program :

Output Screenshot :

Please upvote if it helps. Feel free to comment if you have any query.

***thank you***