Question

Method: DoublyLinkedList reverse(DoublyLinkedList list) Reverse() method accepts a DoublyLinkedList of Character as the argument, reverses the elements in the list, and returns the resulting list. For example:

The given list is

'a' 'b' 'c' 'd' 'e'

The return list should be

'e' 'd' 'c' 'b' 'a'

Answer 1

C++ PROGRAM

#include<iostream>
using namespace std;

// create class for Node
class Node
{
   public:
       // public data members
   char data;
   Node *next,*prev; // reference pointers
};

// implement insert() function with two parameters
// first parameter is Node pointer object head
// second parameter character arguement
void insert(Node **head,char x)
{
   Node *temp=new Node(); // create pointer temp object
  
   temp->data=x; // assign x value to temp object
   temp->prev=NULL; // assign temp->prev=NULL
   temp->next=*head; // assign temp->next=head
  
   if(*head!=NULL) // check head!=NULL
   (*head)->prev=temp; // then, assign head->prev=temp
  
   *head=temp; // finally assign head=temp
}

// implement display() function with single argument

void display(Node *mynode)
{
   Node *last; // declare pointer object last
  
   while(mynode!=NULL) // create while loop mynode is not null
   {
       cout<<mynode->data<<" "; // display mynode data
       last=mynode; // assign mynode to last
       mynode=mynode->next; // repeat mynode->next until NULL
   }
}

// implement reverse() function with single argument
// return pointer Node type
Node * reverse(Node *head)
{
if(head==NULL) // check head=NULL
return head; // then, return head node
Node *temp=head->prev; // create pointer temp node and assign head->prev
while(head) // create while loop until head=NULL
{
   head->prev=head->next; // assign head->next to head->prev
   head->next=temp; // assign temp node to head->next
   temp=head; // assign head to temp
   head=head->prev; // repeate head->prev until NULL
   }
   return temp; // return temp node
  
}

int main()
{
   Node *head=NULL; // create pointer node head and assign NULL
  
   // calling insert() function and insert values into head node
   insert(&head,'e');
   insert(&head,'d');
   insert(&head,'c');
   insert(&head,'b');
   insert(&head,'a');
  
   cout<<"The given list is"<<endl;
   display(head); // calling display() function and display original list
  
   Node *t=reverse(head); // calling reverse() function and receive return Node list
   cout<<"\nThe return list should be"<<endl;
   display(t); // calling display() function and display reverse order list
  
  
  
   return 0;
}

OUTPUT-1

The given list is
a b c d e
The return list should be
e d c b a

OUTPUT-2

If insert two more elements then,

insert(&head,'g');
   insert(&head,'f');
   insert(&head,'e');
   insert(&head,'d');
   insert(&head,'c');
   insert(&head,'b');
   insert(&head,'a');

The given list is
a b c d e f g
The return list should be
g f e d c b a