strategies to reverse a linked list in JavaScript

Question

I just struggled through a simple interview question: Please reverse a singly linked list.

While I failed to provide a working answer in time to save the interview, I was able to come up with a solution afterwards.

Is my solution correct? How would you analyze this with Big-Oh? Are there more efficient ways to reverse a singly linked list?

// reverse a linked list

var reverseLinkedList = function(linkedlist) {
  var node = linkedlist;
  var previous = null;

  while(node) {
    // reverse pointer
    node.next = previous;
    // increment previous to current node
    previous = node;
    // increment node to next node
    if (node.next){
      node = node.next
    } else {
      node = null;
    }
  }
}

Note: In my search for similar posts, I did find one example in JavaScript. I was wondering if my code is possible (without a temp variable). Thank you.

Answer 1

There are a couple of problems with your code. This should make it clear.

// reverse a linked list  
var reverseLinkedList = function(linkedlist) {
  var node = linkedlist;
  var previous = null;

  while(node) {
    // save next or you lose it!!!
    var save = node.next;
    // reverse pointer
    node.next = previous;
    // increment previous to current node
    previous = node;
    // increment node to next node or null at end of list
    node = save;
  }
  return previous;   // Change the list head !!!
}
linkedlist = reverseLinkedList(linkedlist);