Offer 32 - I. 从上到下打印二叉树
1. python
class Solution:
def levelOrder(self, root: TreeNode) -> List[int]:
if not root:
return []
queue = collections.deque()
queue.append(root)
ret = []
while queue:
node = queue.popleft()
if node:
ret.append(node.val)
queue.append(node.left)
queue.append(node.right)
return ret