Postorder Traversal Visualization & Animation

A postorder traversal first visits the left child (including its entire subtree), then visits the right child (including its entire subtree), and finally visits the node itself.

## What is it? Postorder traversal visits every node in a binary tree in **Left → Right → Root** order. The root is visited **last**, after all descendants — making it the natural choice for operations that must process children before their parent. ## How it works - Recursively visit the **left** subtree - Recursively visit the **right** subtree - **Process (visit)** the current node last ``` postorder(node): if node is null: return postorder(node.left) postorder(node.right) visit(node) ← add to result last ``` ## When to use - **Delete a tree** — children must be freed before the parent - **Compute directory sizes** — a folder's size depends on its contents - Evaluate postfix (Reverse Polish Notation) expressions - Bottom-up dynamic programming on trees (e.g., diameter, height, subtree sums) - Any problem where a node's value depends on its subtree results ## Key Points - The last element in postorder output is always the root - Combined with inorder output, postorder uniquely identifies a binary tree - Recursive call stack depth = O(h) - Reverse of preorder on a mirrored tree

Category: algorithms

Difficulty: beginner

Time Complexity: O(n)

Space Complexity: O(h)

Postorder Traversal

beginner

A postorder traversal first visits the left child (including its entire subtree), then visits the right child (including its entire subtree), and finally visits the node itself.

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