Initial call with a recruiter. Set up a phone screen the very next day. Had a technical phone interview with code sharing. Given a BST, print the nodes at each level on a separate line. I could do this easily with a queue, but he wanted something with O(n) time complexity and O(1) space, i.e., no additional data structure like queues, linked lists, or array lists.

Given a BST, print the nodes at each level on a separate line. I could do this easily with a queue, but he wanted something with O(n) time complexity and O(1) space. That is, no additional data structures like queues, linked lists, or array lists.