Preorder Traversal | GeeksforGeeks Beginner's DSA Sheet | Tree Data Structure | With Source Code

hola coders!

In this video, we will break down Preorder Traversal of a Binary Tree step by step and solve a real GeeksforGeeks problem to reinforce our understanding. Preorder Traversal follows the NLR (Node → Left → Right) approach and is one of the fundamental tree traversal techniques used in data structures and algorithms (DSA).

Binary Trees are one of the most crucial topics in Data Structures and Algorithms (DSA), frequently asked in coding interviews at FAANG and top tech companies. Understanding Preorder Traversal is essential because it lays the foundation for solving more complex tree-based problems.

Problem Link: https://www.geeksforgeeks.org/problems/preorder-traversal/1

Source Code: https://github.com/debeshp6/Gfg-Tutorials/blob/main/PreorderTraversal.java

Code

//Back-end complete function Template for Java
class Solution {
    // Function to return a list containing the preorder traversal of the tree.
    static ArrayList<Integer> preorder(Node root) {
        // write code here
        ArrayList<Integer> arr = new ArrayList<>();
        helper(root, arr); // recursion
        return arr;
    }


    // preorder traversal: root - left - right

    static void helper(Node root, ArrayList<Integer> arr) { // we are creating a helper function here
        if(root == null) return; // base case
        arr.add(root.data);
        helper(root.left, arr); // recursion
        helper(root.right, arr);

        // helper function is readyyyy !!!!
    }
}

Time Complexity: O(n)

who should watch this?

• Beginners & Intermediate Programmers – If you are new to trees, this video simplifies the concepts for you
• Competitive Programmers – Improve your problem-solving skills with practical applications
• Job Seekers & Interview Prep Enthusiasts – Preorder Traversal is commonly asked in coding interviews
• DSA Enthusiasts – Strengthen your understanding of fundamental tree traversal techniques

Got any questions? Drop them in the comments below! I’ll be happy to help.

happy coding!