LeetCode 637 Average of Levels in Binary Tree 解题报告

题目要求

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

题目分析及思路

给定一棵非空二叉树，要求以列表的形式返回每一层结点值的平均值。可以使用队列保存结点，进行层次遍历，要特别注意空结点的判断。

python代码

# Definition for a binary tree node.

# class TreeNode:

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution:

    def averageOfLevels(self, root: TreeNode) -> List[float]:

        aves = []

        q = collections.deque()

        q.append(root)

        while q:

            level = []

            size = len(q)

            count = 0

            for _ in range(size):

                node = q.popleft()

                if not node:

                    count += 1

                    continue

                level.append(node.val)

                q.append(node.left)

                q.append(node.right)

            if size-count != 0:

                aves.append(sum(level)/(size-count))

        return aves