958. Check Completeness of a Binary Tree

Python

BFS

from collections import deque


class Solution:
    def isCompleteTree(self, root: Optional[TreeNode]) -> bool:
        queue = deque([root])

        while queue:
            node = queue.popleft()

            if node:
                queue.append(node.left)
                queue.append(node.right)
                continue
            while queue:
                if queue.popleft():
                    return False
        return True