Tree Traversal

Inorder · Preorder · Postorder · Level Order

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Four systematic rules — in-order, pre-order, post-order, and level-order — for visiting every node in a tree exactly once, and how to pick the right one for the job.

By the end, you can

Explain why trees need an explicit traversal rule when linked lists do not.
Describe the recursive DFS template and show how moving the visit line produces each of the three DFS orders.
Trace in-order, pre-order, and post-order traversals on a binary tree by hand, producing the correct node sequence.
Trace a level-order (BFS) traversal by simulating the queue step by step.
Identify the data structure (stack vs queue) that drives each traversal family.
Match each traversal to its primary use case: in-order for sorted output, pre-order for serialization, post-order for deletion, level-order for shortest path.
State the time and space complexity of each traversal and explain why depth-first and breadth-first differ in space usage.

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