LC 0102 [M] Binary Tree Level Order Traversal - ALawliet/algorithms GitHub Wiki

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# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def levelOrder(self, root: TreeNode) -> List[List[int]]:
        if not root: return []
        
        levels = []
        
        Q = deque([root])
        
        while Q:
            # enter the current level
            level_size = len(Q)

            nodes_in_level = []
            
            # range across the level
            for _ in range(level_size):
                node = Q.popleft()

                nodes_in_level.append(node.val)
                
                if node.left:
                    Q.append(node.left)
                if node.right:
                    Q.append(node.right)
                    
            levels.append(nodes_in_level)
            
        return levels