symmetric-tree.py

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        
        queue = []
        queue.append(root)
        
        while all(node is None for node in queue) == False:
            if [i.val if i is not None else None for i in queue] == [i.val if i is not None else None for i in queue][::-1]:
                num_to_remove = len(queue)
                for j in range(num_to_remove):
                    if queue[j] is not None:
                        queue.append(queue[j].left)
                        queue.append(queue[j].right)
                    else:
                        queue.append(None)
                        #queue.append(None) # 注释掉之后就神奇的不超时了
                for k in range(num_to_remove):
                    queue.pop(0)
            else:
                return False
        
        return True