I started with a quick phone call from a recruiter at Facebook. He was very nice and polite but not technical. The questions were related to past experience, but I felt as though it was more just a quick fit check before moving to a more technical interview.

My next step was a call with a Senior Engineer. The phone call lasted about an hour, during which you will be quizzed on elementary data structures and algorithms.

Create an iterator to traverse a binary tree. When the next function is called on the binary tree, return the value at the next node as if you are doing an inorder traversal of the tree.

Restrictions:

• Nodes do not have pointers to their parent node.
• You cannot use recursion.