How Would You Reverse A Linked List?

How Would You Reverse A
Linked List?

Reversing the linked list
is the most critical and exciting data structure and algorithms issue. The lack
of awareness about the reverse linked list is the primary reason behind the
problem. Here, reversing the linked list means reassigning all the following
properties on each node. Do you want to know in-depth about how to change the
linked list? Scroll down the page. 

What Does The Reverse
Linked List Mean?

The reverse linked list is
the link list developed to form the linked list by reversing the list’s links.
The head node of the linked list will become the last note of the linked list
and vice versa. In simple words, the node present in the terminal end will come
to the front. You can reverse the linked list using recursion and iterative
methods. Here is an example of a reverse linked list.

Input:
1->2->3->4->5->NULL

Output:
5->4->3->2->1->NULL

It is necessary to use
three extra pointers that will be in the process to reverse the given linked
list. The pointers will be current, previous, and after. Initially, you have to
initialize previous and after to NULL. Then, initialize current to the head of
the linked list. Next, you must iterate until reaching the NULL of the initial.
It is precisely the same mentioned below.

after = current ->

next current ->

next = previous

previous = current

current = after

Different Ways To Reverse
The Linked List

You can reverse the linked
list either using the iterative approach or the recursion approach. In the
following section, you will learn in-depth about both processes. You can choose
the specific method and then reverse the linked list according to your
requirements.

• Iterative Approach

In this way, the new linked
list will create, and all the elements of the first linked list will add to the
new linked list in the reversal order. It is the most efficient way among the
methods listed here.

Although objects of every
node are copied to memory, the new linked list node creates for every call to
add a property. It needs at least three-pointers to create the new link list.
Even though this method does not waste memory, it consumes more processing
power. 

Read also What are Solid State Drives (SSDs)?

When the linked list has
two or more elements, three-pointers must be used to implement the iterative
solutions. Ensure you use the function to reverse the linked list. Then, you
have to pass the head pointer as the sole argument. It will return to the head
of the reversed list. 

Afterward, you must assign
three nodes – prev (with null pointers), current (concerning the head node),
and temp. Access the while loop to traverse the linked list until the next
pointer does not yield NULL. The following operations will perform in the
iterative process.

temp = current->next;

• • Assigns temp node to the current node’s
    next node

current->next = prev;

• • Assigns current node to the previous
    node’s next node

prev = current;

• • Increments previous node to current
    node

current = temp;

• • Increments current node to temp node

Finally, you will return to
the head node of the reversed list. It indicates the completion of the process
of reversing the linked list. 

Steps To Follow 

If you choose the iterative
approach to reverse the linked list, you should carefully follow these steps.

• Take the three-pointers and initialize
  them like previous = NULL, next = NULL, and current = head.
• Use the loop to iterate the linked list
  and then perform the below-mentioned.

// before changing the next
of the current,      

 // keep the next
node       

next = current ->
next      

// Now changing the next of
current      

// it is where the
reversing takes place      

current -> next =
previous       

// Moving the previous and
current forward for one step     

Previous = current

Current = next

• Recursion Approach

You have to divide the
linked list into two parts – the head and the remaining. Initially, the head
points to the first element, and the next element from the head indicates the
remaining.

After the reversal, the
next mode of the head will become the last node. Then, the head will point to
that node. However, the head must be the last node for the complete reversal
linked list. After that, link the rest to the first and fix the head pointer.
Follow the below operation to ensure this.

head.next.next = head

head.next = NULL

Note: You should save the
copy of the head so as not to lose track of the original head. 

The recursive solution
accesses the stack because the recursive solution will run out of memory,
especially when working with an extensive linked list. So, every recursive call
needs your complicate to allocate the stack memory. 

It would help if you
visited every node in the given linked list until reaching the last node to
return the head of the new linked list. Then, this node serves as the new head
of the linked list. Every node appends itself to the end of the partially
reversed list on the return path. It means every node should iterate through
every element at least once.

How To Reverse The Linked
List Using Stack 

When you decide to reverse
the linked list using stack, you should follow these steps. 

• Keep the nodes’ values in the stack
  until you enter all the nodes’ values. 
• Use the value of the last note of the
  linked list to update the head pointer. 
• Keep eliminating the value of the nodes
  from the stack and begin adding them to the head stack, which is empty.
• As soon as the appending work is
  completed, the last node of the linked list points to NULL. It means the
  reversal process using the stack is successful. 

Use The Swapping Method To
Reverse The Link List.

You can even use another
technique to reverse the linked list. In that method, you will swap linked list
note objects. You can start the swapping from the first node’s object, and the
object of the first node is swapped with the last node’s object. 

After that, the object of
the second note is swapped with the one before the last node’s element. The
swapping process goes on until it reaches the linked list’s middle. It is one
of the fastest and most optimized reversing the linked list. The overhead of
the algorithm is locating the end of the linked list. 

Whether or not you have
prior knowledge on reversing the linked list, it is better to seek professional
assistance. So, contact JDM Web Technologies today.