LeetCode 637 Average of Levels in Binary Tree 解题报告

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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