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Binary Tree Level Order Traversal

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 10

Write a JavaScript program to perform level order traversal of a binary tree. Given the root of a binary tree, return the level order traversal of its nodes' values as a 2D array where each sub-array represents one level of the tree.

Example 1
    
  
  • Input: root = [3,9,20,null,null,15,7]
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  • Output: [[3],[9,20],[15,7]]
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  • Explanation: 
    • The root node 3 is at level 0. 
    • Nodes 9 and 20 are at level 1, children of node 3. 
    • Nodes 15 and 7 are at level 2, children of node 20. 
    • Each level is collected into separate arrays: [3], [9,20], [15,7].
    •
Example 2
    
  
  • Input: root = [1]
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  • Output: [[1]]
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  • Explanation: 
    • The tree contains only the root node. 
    • Node 1 is at level 0. 
    • The result contains one level with one element: [1]. 
    • Final output is [[1]].
    •
Constraints
    
  
  • The number of nodes in the tree is in the range [0, 2000]
    • 
  
  • -1000 ≤ Node.val ≤ 1000
    • 
  
  • Time Complexity: O(n)
    • 
  
  • Space Complexity: O(n)
    •
QueueAppleD. E. Shaw
Editorial

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Hint
Solution

Solution Hints

    
  
  • Use a queue data structure to implement breadth-first search (BFS)
    • 
  
  • Start by adding the root node to the queue
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  • For each level, process all nodes currently in the queue
    • 
  
  • Add children of current level nodes to the queue for the next level
    • 
  
  • Store each level's values in a separate array
    •

Steps to solve by this approach:

  Step 1: Handle the edge case where the root is null by returning an empty array.

 Step 2: Initialize a result array to store levels and a queue with the root node for BFS traversal.

 Step 3: Continue processing while the queue contains nodes to visit.

 Step 4: Record the current queue size to know how many nodes belong to the current level.

 Step 5: Process all nodes in the current level by dequeuing them and adding their values to the current level array.

 Step 6: Add the left and right children of each processed node to the queue for the next level.

 Step 7: Add the completed current level array to the result and repeat until all levels are processed.

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