958.Check Completeness of a Binary Tree

tags: Medium,Tree,BFS

958. Check Completeness of a Binary Tree

題目描述

Given the root of a binary tree, determine if it is a complete binary tree.

In a complete binary tree, every level, except possibly the last, is completely filled, and all nodes in the last level are as far left as possible. It can have between 1 and 2^h nodes inclusive at the last level h.

範例

Example 1:

Input: root = [1,2,3,4,5,6]
Output: true
Explanation: Every level before the last is full (ie. levels with node-values {1} and {2, 3}), and all nodes in the last level ({4, 5, 6}) are as far left as possible.

Example 2:

Input: root = [1,2,3,4,5,null,7]
Output: false
Explanation: The node with value 7 isn't as far left as possible.

Constraints:

• The number of nodes in the tree is in the range [1, 100].
• 1 <= Node.val <= 1000

解答

Python

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

        while dq:
            node = dq.popleft()

            if not node:
                null_node_found = True
            else:
                if null_node_found:
                    return False

                dq.append(node.left)
                dq.append(node.right)

        return True

Ron Chen Wed, Mar 15, 2023

Reference

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