Preorder Traversal Explained

Preorder traversal is a method used to traverse a binary tree by visiting nodes in the following order:

1. Root Node
2. Left Subtree
3. Right Subtree

This traversal is particularly useful for tasks such as copying a tree, expression evaluation, or converting the tree into another structure.

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Characteristics

• Depth-First Approach: Visits nodes deeply before backtracking.
• Top-Down Order: Processes the root first, then recursively visits the left and right subtrees.
• Implementation Flexibility: Can be implemented recursively or iteratively using a stack.

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How Preorder Traversal Works

1. Visit the Root: Start with the root node of the tree.
2. Traverse the Left Subtree: Recursively perform a preorder traversal on the left subtree.
3. Traverse the Right Subtree: Recursively perform a preorder traversal on the right subtree.

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Test Cases

Test Case 1: Simple Tree

Input Tree:

Expected Output:
[1, 2, 4, 5, 3]

Test Case 2: Tree with One Child Nodes

Input Tree: Expected Output:
[10, 20, 30, 40]

Summary

Preorder traversal follows the order Root → Left → Right. It is a simple and effective method for visiting all the nodes in a tree, ensuring that the root is processed before its children. This method is essential in various tree-related operations and helps in understanding the hierarchical structure of data.