Get a NON thread-safe iterator over the nodes in the tree for a DFS ordering.
Get a NON thread-safe iterator over the nodes in the tree for a DFS ordering. Each iterator value contains the node in the tree and the depth (root has 0 depth). This iterator requires O(B * D) auxiliary space where B is the branching factor and D is the tree depth.
a NON thread-safe iterator over the nodes in the tree for a DFS ordering.