Reverse Linked list giving wrong answer

Question

I have the following code to reverse linked list But I am getting NPE at head.next = prev; How can I resolve it?

    ListNode l = new ListNode();
            l.insert(4);
            l.insert(10);
            l.insert(12);

            l.show();
            l.reverse();
            l.show();

public void reverse() {
        ListNode nextNode = null;
        ListNode curr = head;
        ListNode prev = null;

        while (curr != null) {

            nextNode = curr.next;
            curr.next = prev;
            prev = curr;
            curr = nextNode;
        }

        head = curr;
        head.next = prev;

    }

head = curr; is also done if curr is null. most likely, there's your problem (at least one) — Stultuske, Sep 02 '19 at 11:12

score 0 · Answer 1 · answered Sep 02 '19 at 11:15

0

you're checking for curr to be null or not while you should check for curr.next to be null or not.

answered Sep 02 '19 at 11:15

Ali Ben Zarrouk

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score 0 · Answer 2 · answered Sep 02 '19 at 11:25

I am on mobile but what I see in the first go is...

head = curr; is out of while loop which means null will also be added to head and in next line

head.next = prev; we have an operation performed with 'dot'. That would lead to failure I feel.

is it the only issue??

Reverse Linked list giving wrong answer

2 Answers2