102_Binary_Tree_Level_Order_Traversal.py

from collections import deque
from typing import List, Optional 

class Node:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

class Solution:
    def levelOrder(self, root: Optional[Node]) -> List[List[int]]:
        if not root:
            return []
        result = []
        queue = deque([root])

        while queue:
            level_size = len(queue)
            current_level = []

            for _ in range(level_size):
                node = queue.popleft()
                current_level.append(node.val)

                if node.left:
                    queue.append(node.left)
                
                if node.right:
                    queue.append(node.right)
            result.append(current_level)

        return result
    
if __name__ == "__main__":
    root = Node(3)
    root.left = Node(9)
    root.right = Node(20)
    root.right.left = Node(15)
    root.right.right = Node(7)

    print(Solution().levelOrder(root))