力扣：101. 对称二叉树

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def isSymmetric(self, root: TreeNode) -> bool:
        from queue import Queue
        qu = Queue()
        qu.put(root)
        while not qu.empty():
                    # q 如果存本层节点的数值，就不完整，判断不了对称性
            q = [] # q存的是这层节点的所有子节点的数值，如果空就存None
            s = qu.qsize()
            for i in range(s):
                a = qu.get()
                if a.left:
                    qu.put(a.left)
                    q.append(a.left.val)
                else:
                    q.append(None)
                if a.right:
                    qu.put(a.right)
                    q.append(a.right.val)
                else:
                    q.append(None)
            for i in range(len(q)//2):
                if q[i] != q[len(q) - i - 1]:
                    return False
        return True