Why head getting changed even though i copy it in another Node called curr.? It's happening only after reversing my linked List.

Question

https://code.sololearn.com/c8xj8PTuAL2f/?ref=app

Answer 1

Comment line 36:
current.next = prev; will set head.next to prev which is null.

Answer 2

That is to reverse linked list right if i comment it mu linked list won't get reversed.

Answer 3

If we need to reverse, head node should become tail node(tail node address is null). curr.next does this, while looping i make move prev and head one node right.

Answer 4

So Even if i copy head to curr node and use it, changes made in curr node will alse change head. Am I right? Mr.Jayakrishna

Answer 5

Yes.
As per your method, how you go back to previous node. You don't have previous node for your Node object..? I think it's not work.
What is your reverse() method do?

Answer 6

Node curr = head;
Node prev = null;
While(curr != null){
//Storing node next to head in nextNode.
so that we won't loose data.
Node nextNode = curr.next;

//Now the curr.next made null(so that it becomes tail)
curr.next = prev;
//Now the current Node is made as prev.
(this is my previous node now)
prev = curr;

//Now the previously next Node is made as current head Node.
(this is my head node now)
curr = nextNode;
}

Answer 7

Prev is my reversed linked list.

Answer 8

" curr.next made null ( so that it becomes tail) "
How it becomes tail? Tail is the last node your added which last 1.
1-> 2->1->1
If current is 1 then next is 2
Every time you copy current into prev because at last curr.next becomes null at loop end.
By this method, you are finding last entered value, not previously entered value...

And Yes.
curr = head; copies references..

Answer 9

1->2->3

prev. curr.
null. 1:ptr2 -> 2:ptr3 -> 3:null
nextNode = curr.next.(i.e., Node 2:ptr3)

curr.next = prev;
Prev = curr

prev
null:1. 2:ptr3-> 3: null

Curr = nextNode

prev. curr
null:1 2:ptr3 -> 3:null
-----------------------------------------------------------------------
prev. curr.
null:1 2:ptr3 -> 3:null
nextNode = curr.next.(i.e., Node 3:null)

curr.next = prev;
Prev = curr

prev
null:1<-2:ptr1 3: null

Curr = nextNode

prev. curr
null:1<-2:ptr3 3:null
--------------------------------------------------
prev. curr.
null:1<-2:ptr3 3:null
nextNode = curr.next.(i.e., null)

curr.next = prev;
Prev = curr

prev
null:1<-2:ptr1 <-3: ptr2

Curr = nextNode

prev. curr
null:1<-2:ptr1 <-3:ptr2. null
-----------------------------------------------

prev = 3:ptr2 -> 2:ptr1->1:null
Curr = head = null.

Answer 10

I understood how head becomes null

Answer 11

Thank you so much for your Answers

Answer 12

Your pointings are not clear to me..

1->2->3
Node prev = null;

Node nextNode = curr.next;
curr.next = prev;
prev = curr;
curr = nextNode;

Prev : curr.val
Null : 1

First line in loop,
Node nextNode = curr.next;

stores your next node (2) into newNode..

curr.next = prev; this assigns curr to null ( so head.next also assigned to null).

Next
Prev = curr assign null pointer but prev.val is still 1

Curr = nextNode ; this stores back next node ->2
______________

Node nextNode = curr.next;

stores your next node (3) into newNode..

curr.next = prev; this assigns Node(2) pointer which is due to prev<=curr<=newNode previous iteration.

Next
Prev = curr assign Node(2) to prev

Curr = nextNode ; this stores back next node ->3
________

Node nextNode = curr.next;

stores null end node into newNode..

curr.next = prev; this assigns Node(3) pointer which is due to prev<=curr<=newNode previous iteration.

Next
Prev = curr assign Node(3) to prev

Curr = nextNode \\ null

Answer 13

If you comment curr.next = prev then it won't set null and head as well..
But curr getting back next node because of
curr = nextNode;
But here head is no longer pointing to curr. So won't affect on head...

Hope it helps..

Answer 14

I understood the mistake there. Thank you for your Answers.

Answer 15

This is how my code works

Answer 16

Can you clarify me your above point (because i am still confused) with my explanation or correct me if i am wrong

Answer 17

Curr.next stores the previous nodes address.

If I comment curr.next = prev;
I won't get reversed Linked list.

And as per my code my head should become null. As i create new linked list (which is reversed) prev.

So I have to do inplace reversing to get
Head itself as my reversed linked list.