python--leetcode637. 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:

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

题目意思很简单，无非就是给你一棵树，让你求每层的平均值。

思路如下，开两个数组，第一个记录每层数的总和，另一个记录每层的结点个数。递归遍历整棵树就好。

# 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]
        """
        sum=[0.0 for i in range(1000)]
        count=[0.0 for i in range(1000)]
        num=0
        def all(root,num):
            if root:
                sum[num]=sum[num]+root.val
                count[num]=1+count[num]
                all(root.left,num+1)
                all(root.right,num+1)
        all(root, num)
        res=[]
        for i in range(len(sum)):
            if count[i]!=0:
               res.append(sum[i]/count[i])
        return res



s=Solution()
Tree=TreeNode(3)
Tree.left=TreeNode(9)
Tree.right=TreeNode(20)
Tree.right.left=TreeNode(15)
Tree.right.right=TreeNode(7)
print(s.averageOfLevels(Tree))

这应该是最简单且明了的解法。

原文链接：https://blog.csdn.net/wenqiwenqi123/article/details/78162099