CareerCup

Find the issue with the above code and fix it.

pnode ReversLinklist(Linklist s)
{
pnode p=s;
pnode q,r;
if(p==NULL) return NULL;
if(p->next==NULL ) return p;
q=p->next;
while (q!=NULL)
{ if(q->next!=NULL)
{
r=q->next;
q->next=p;
if (p==s)
{
p->next=NULL;
}
p=q;
q=r;
}
else
{
q->next=p;
return q;
}
}
}

I can't find any issue from original code if the linked list does not contains any loop.

Problems are :
1. As mentioned by Dinesh,
2. No iterator used to iterate through linkedlist

public static LinkedList<Integer> reverse(LinkedList<Integer> current)
    { 
        LinkedList<Integer> result = new LinkedList<Integer>();
        if (current == null) {
            return null;
        }

        Iterator<Integer> li = current.iterator();
        while (li.hasNext()) {
            int next = li.next();
            result.addFirst(next);
        }
        return result;
    }

the code is always loosing the head element in the iteration

Suppose we have following list

a -> b -> c -> d

So the reverse would be like this

d-> c-> b

public void reverse()
        {
            Node<E> temp=head;
            head=tail; // //swap head and tail
            tail=temp; //tail points to head
            //traverse the list swapping prev and next fields of each node
            Node<E> p=head; //create a node and point to head

            while(p!=null) //while p does not equal null
            { //swap prev and next of current node

                temp=p.next;
                p.next=p.prev; //point next pointer to previous
                p.prev=temp;     //previous point to what next used to point to
                p=p.next;//advance current node
            }

        }

Code is wrong..

Suppose we have following list

a -> b -> c -> d

After first while loop it will be

b-> null -> c-> d

Third time loop will not execute..