When looking at a question of this magnitude, there are a number of different factors to consider. You will want to get clarification from the interviewer on whether they want to hear the meaning for tree structure data, time complexity, extra space, or a node stack. Let's examine what some of these mean and how they might come up in the course of an interview. Time Complexity - has four transversals O(n) as they visit every node exactly once. Extra Space - requires O(w) Level Order Transversal where w is the maximum width of a Binary Tree which stores nodes of different levels. Interview related questions might look something like.....what are typical binary tree numbers? 1, 3, 7, 15 or in a worst case scenario a value of 2h is Ceil(n/2) will usually come up as good answers to this question. A couple more that might come are when is extra space required for Level Order Transversal and Depth First Transversal? Two good responses can be a more balanced position for Level Order Transversal, and a less balanced position for Depth First Transversal.