以下代码可以正确地按层换行输出二叉树的节点值。（ ）
from collections import deque
class TreeNode:
def __init__(self, val=0, left=None, right=None):
self.val = val
self.left = left
self.right = right
def printByLevel(root):
if not root:
return
q = deque([root])
while q:
for i in range(len(q)):
cur = q.popleft()
print(cur.val, end=' ')
if cur.left:
q.append(cur.left)
if cur.right:
q.append(cur.right)
print()
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