Check two balanced binary search trees that sub set of each other
When you try to traverse a tree, you start at the root, and you will have to remember all the nodes that you were visiting, to be able to find the next node. If your tree is balanced, then it contains only O (log n) nested notes, so your space requirement for two trees is only O(log n) + O(log m). Unbalanced trees could be nested up to n levels deep, so you could need up to O(n) + O(m) space to traverse both trees.