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Binary Tree Level Order Traversal

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

Write a Java program to return the level order traversal of a binary tree's node values. That is, from left to right, level by level.

Example 1
    
  
  • Input:

    Binary Tree Level Order Traversal with root node 3

    • 
  
  • Output: [[3], [9, 20], [15, 7]]
    • 
  
  • Explanation: 
    
      
      
    • Level 0 contains node with value 3.
      • 
      
    • Level 1 contains nodes with values 9 and 20, from left to right.
      • 
      
    • Level 2 contains nodes with values 15 and 7, from left to right.
      • 
      
    • Combine all levels into a list of lists: [[3], [9, 20], [15, 7]].
      • 
    
    
  
    •
Example 2
    
  
  • Input: 
    
      
      
    • Tree: 
            1
      
      • 
    
    
  
    • 
  
  • Output: [[1]]
    • 
  
  • Explanation: 
    
      
      
    • Level 0 contains only the root node with value 1.
      • 
      
    • There are no other levels.
      • 
      
    • Result is [[1]].
      • 
    
    
  
    •
Constraints
    
  
  • The number of nodes in the tree is in the range [0, 2000]
    • 
  
  • -1000 ≤ Node.val ≤ 1000
    • 
  
  • Time Complexity: O(n), where n is the number of nodes in the tree
    • 
  
  • Space Complexity: O(n), to store the result and the queue during traversal
    •
Binary TreePwCApple
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Hint
Solution

Solution Hints

    
  
  • Use a breadth-first search (BFS) approach using a queue
    • 
  
  • Process nodes level by level, starting from the root
    • 
  
  • Keep track of the number of nodes at each level
    • 
  
  • Add all nodes at the same level to a separate list
    • 
  
  • Consider using two queues to differentiate between levels, or use sentinel nodes to mark level boundaries
    •

Steps to solve by this approach:

 Step 1: Create a result list to store the level order traversal.
 Step 2: If the root is null, return an empty result.
 Step 3: Use a queue to perform breadth-first search, starting with the root node.
 Step 4: For each level, determine the number of nodes at that level (queue size).
 Step 5: Process each node at the current level, adding its value to the current level list.
 Step 6: Add the children of the current node to the queue for processing in the next level.
 Step 7: Add the completed level list to the result and continue until the queue is empty.

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