reverse - Reversing single linked list in C#

Question

I am trying to reverse a linked list. This is the code I have come up with:

 public static void Reverse(ref Node root)
 {
      Node tmp = root;
      Node nroot = null;
      Node prev = null;

      while (tmp != null)
      {
          //Make a new node and copy tmp
          nroot = new Node();    
          nroot.data = tmp.data;

          nroot.next = prev;
          prev = nroot;   
          tmp = tmp.next;
       }
       root = nroot;            
  }

It is working well. Was wondering if it possible to avoid creating new node. Would like to have suggestions on this.

Answer 1

That question gets asked a lot. When I was asked it in my interviews many years ago, I reasoned as follows: a singly-linked list is essentially a stack. Reversing a linked list is therefore a trivial operation on stacks:

newList = emptyList;
while(!oldList.IsEmpty())
    newList.Push(oldList.Pop());

Now all you have to do is implement IsEmpty and Push and Pop, which are one or two lines tops.

I wrote that out in about twenty seconds and the interviewer seemed somewhat perplexed at that point. I think he was expecting me to take about twenty minutes to do about twenty seconds work, which has always seemed odd to me.