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Binary Tree Level Order Traversal

Explore how to implement a binary tree level order traversal with breadth-first search. Understand how to traverse each level efficiently, return node values separated by colons, and handle edge cases like empty trees.

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Statement

Given the root of a binary tree, display the values of its nodes while performing a level order traversal. Return the node values for all levels in a string separated by the character :. If the tree is empty, i.e., the number of nodes is 00, then return “None” as the output.

Constraints:

  • The number of nodes in the tree is in the range [0,500][0, 500].

  • −103≤-10^3 \leq Node.data ≤103\leq 10^3

Examples

Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

Technical Quiz
1.

How does BFS ensure that it visits all nodes in a binary tree while traversing level by level?

A.

By using a stack data structure to keep track of visited nodes

B.

By using a queue data structure to maintain the order of node exploration

C.

By recursively traversing the left and right subtrees in a depth-first manner

D.

By randomizing the order of node exploration for better coverage

1 / 3

Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
1
2
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5

Try it yourself

Implement your solution in the following coding playground.

Note: The binary tree node’s class has members left and right to store references to other nodes, along with the member data to hold the node’s value.

Java
usercode > Solution.java
// Definiton of a binary tree node class

// class TreeNode<T> {

//     T data;

//     TreeNode<T> left;

//     TreeNode<T> right;



//     TreeNode(T data) {

//         this.data = data;

//         this.left = null;

//         this.right = null;

//     }

// }



import java.util.*;

import ds_v1.BinaryTree.TreeNode;



public class Solution{

    public static String levelOrderTraversal(TreeNode<Integer> root) {

    

      // Replace this placeholder return statement with your code

      return "";

  }

}
Binary Tree Level Order Traversal