Binary Tree Level Order

👶 The 5-Year-Old Summary

Visit a tree level by level! First the grandparents, then parents, then children! Like taking an elevator that stops at each floor!

🎮 Interactive Visualizer

Breadth-First Search (BFS) with a queue!

Queue:

Result Levels:

🧠 The Brain Hack

Use a QUEUE! Add root to queue. While queue not empty, process all items in queue (that's one level!), add their children for next level!

💻 The Clean Solution

from collections import deque

def level_order(root):
    if not root: return []
    
    result = []
    queue = deque([root])
    
    while queue:
        level_size = len(queue)
        level = []
        
        for _ in range(level_size):
            node = queue.popleft()
            level.append(node.val)
            
            if node.left: queue.append(node.left)
            if node.right: queue.append(node.right)
        
        result.append(level)
    
    return result

# Tree:     3
#          / \
#         9  20
#           /  \
#          15   7
# Result: [[3], [9, 20], [15, 7]]

Time: O(n)

Space: O(w) - max width