In a preorder traversal, we need to visit the root node first, then all left child nodes, followed by the right child nodes. We can take the root's left and right subtrees as a subproblem and ...

Given a binary tree, return the preorder traversal of its nodes' values. Example: Input: [1,null,2,3] 1 \ 2 / 3 Output: [1,2,3] Follow up: Recursive solution is trivial, could you do it iteratively ...

Is there any way to implement a nonrecursive preorder traversal of a binary tree without using a stack? In a standalone function?the recursive preorder ...