Recursive vs Iterative Tree Traversals: Understanding the Stack Behind the Magic

Tree traversals are a common interview challenge, and many developers rely on recursive solutions without fully understanding how they work under the hood. The core insight is that recursive traversal uses the call stack to track return points, and this behavior can be replicated with an explicit stack data structure. In an iterative inorder traversal, nodes are pushed left as far as possible, then popped and visited before moving to the right subtree — mirroring the recursive left-node-right pattern. This approach avoids stack overflow errors that can occur with deeply skewed trees containing large numbers of nodes. Two common pitfalls in iterative implementations are failing to advance the current pointer after popping a node, and pushing children in the wrong order, both of which can cause incorrect output or infinite loops.