Binary Tree Traversal – Inorder, Preorder, Postorder Explained

In inorder traversal we visit left subtree, then root, then right subtree — for a BST this gives nodes in sorted order. Preorder visits root first, then left, then right — useful for serializing or copying a tree. Postorder visits left, right, then root — ideal for deleting a tree or evaluating postfix expressions. Recursively, each is a simple three-line function that changes only the order of the recursive calls and the visit step. Iteratively, inorder uses a stack: push all left children, pop and visit, then move to the right child. Preorder pushes root, pops and visits, then pushes right before left. Postorder can be done with two stacks or by reversing a modified preorder. All three run in O(n) time and O(h) space where h is the tree height. I always mention the iterative versions because they show you can convert recursion into explicit state management, which matters for very deep trees.