DSA SERIES | Linked List | LECTURE 12 | LEETCODE PROBLEM 144

🚀 DSA SERIES | Lecture 12 | LeetCode 144: Binary Tree Preorder TraversalWelcome to the twelfth lecture of our Data Structures & Algorithms (DSA) Series! Today, we are diving deep into the world of Trees by mastering the first of the three primary DFS traversals: Preorder Traversal. In this session, we break down LeetCode 144 - Binary Tree Preorder Traversal.As visualized in the thumbnail watermarked_img_16249870316267235470.png, we are exploring the recursive structure of a binary tree and how to systematically visit every node.💡 In this lecture, you’ll learn:Stage 1: Root Access: Understanding why Preorder means visiting the Root first before moving to any children.Stage 2: Recursive Left Subtree Call: Navigating down the left branch to process all sub-nodes in $O(N_{left})$ time.Stage 3: Recursive Right Subtree Call: Returning to process the right branch once the left side is exhausted.Final Merge and Return: How to combine results from both subtrees to return a final O(N) time total traversal.Recursive vs. Iterative: A quick look at how the Call Stack (from Lecture 6) handles these recursive calls behind the scenes.
🎯 Preorder traversal is essential for tasks like copying a tree or evaluating prefix expressions. It is a fundamental building block for almost all advanced tree problems you will face in coding interviews.
🔥 Master the flow of recursion and learn to traverse trees like a pro!
📌 Missed Lecture 11? Watch the "Linked List Cycle II" solution here:
https://youtu.be/6E3xT3nJO3Q?si=IdgXvQJf0_JTxc5X.
📌 Coming Up Next: We tackle Inorder Traversal (LeetCode 94) and see how the order of visits changes the result!Quick Question: In a Preorder traversal, if a node has no children, what is the next step in the recursion? Let me know in the comments! 👇
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