题解 | #判断是不是完全二叉树#

层次遍历。

class Solution:
    def isCompleteTree(self , root: TreeNode) -> bool:
        if not root:
            return True
        
        s = []
        s.append(root)
        flag = False

        while len(s):
            for i in range(len(s)):
                node = s[0]
                s.pop(0)

                if not node: 
                    flag = True
                else:
                    if flag:
                        return False
                    s.append(node.left)
                    s.append(node.right)
        
        return True