In-order Traversal: Iterative Implementation

Exercise Open the starter code and complete the implementation of BstOrderedSet.iterator.

Hint 1: You cannot do this recursively (in Java). The iterator needs to "pause," so to speak, and wait for a call to next to generate (retrieve) the next element.

Hint 2: You will need an auxiliary data structure in the iterator class to keep track of some of the nodes as you traverse the tree so that you can visit those nodes later. This auxiliary data structure will make a less efficient iterator (space complexity greater than $O(1)$).