- 深度优先用递归

- 广度优先用循环队列(一边出一边入)

# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @return bool布尔型
#
class Solution:
    def isCompleteTree(self , root: TreeNode) -> bool:
        if root is None:
            return True

        l = [root]
        # 是否遇到空节点
        f = False

        while len(l) > 0:
            now = l.pop(0)

            # 遇到空节点就记录下
            if now is None:
                f = True
            else:
                # 遇到之后还有不是空节点的就不是完全二叉树
                if f: return False
                l.append(now.left)
                l.append(now.right)

        return True