Two Approaches to Binary Tree Preorder Traversal Explained with Java Code

Preorder traversal of a binary tree follows the Root → Left → Right sequence, visiting the current node before its subtrees. A recursive solution naturally mirrors this order, achieving O(N) time and O(H) space complexity, where H is the tree's height. An iterative alternative uses a stack, pushing the right child before the left so the left subtree is popped and processed first. Both approaches produce the same traversal result and share identical time and space complexity. The iterative stack-based method is particularly useful for simulating recursion in interview settings without relying on the call stack.