Preorder Traversal Visualization & Animation

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

## What is it? Preorder traversal visits every node in a binary tree in **Root → Left → Right** order. The root is always visited **first**, before any children — making it ideal for copying or serializing a tree structure. ## How it works - **Process (visit)** the current node first - Recursively visit the **left** subtree - Recursively visit the **right** subtree ``` preorder(node): if node is null: return visit(node) ← add to result first preorder(node.left) preorder(node.right) ``` ## When to use - **Copy / clone** a tree — inserting preorder output into a new BST reconstructs the same structure - **Serialize** a tree to a string (with null markers, it is fully reversible) - Print or display hierarchical structures (directory trees, XML/HTML DOM) - Evaluate prefix (Polish notation) expressions ## Key Points - The first element in preorder output is always the root - Combined with inorder output, preorder uniquely identifies a binary tree - Recursive call stack depth = O(h) - Used in compilers to generate prefix notation from expression trees

Category: algorithms

Difficulty: beginner

Time Complexity: O(n)

Space Complexity: O(h)

Preorder Traversal

beginner

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

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