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   7Output: [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 = Noneclass 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 ress=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。