题目描述：

LeetCode 637. Average of Levels in Binary Tree

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

Example 1:

Input:
    3
   / \
  9  20
    /  \
   15   7
Output: [3, 14.5, 11]
Explanation:
The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

Note:

1. The range of node's value is in the range of 32-bit signed integer.

题目大意：

求二叉树每层节点的均值

解题思路：

二叉树层次遍历

Python代码：

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def averageOfLevels(self, root):
        """
        :type root: TreeNode
        :rtype: List[float]
        """
        ans = []
        que = [root]
        while que:
            ans.append(1.0 * sum([n.val for n in que]) / len(que))
            nque = []
            for n in que:
                if n.left: nque.append(n.left)
                if n.right: nque.append(n.right)
            que = nque
        return ans

 

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