题目
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.
难度
Easy
方法
对二叉树进行深度遍历，将深度level作为参数传递，记录每一级的sum和个数n，最后将sum/n保存到结果列表中即可
python代码
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]
"""
sums = []
nums = []
def dfs(node, level):
if node:
if len(sums) <= level:
sums.append(0)
nums.append(0)
sums[level] += node.val
nums[level] += 1
dfs(node.left, level+1)
dfs(node.right, level+1)
dfs(root, 0)
result = []
for i in range(len(sums)):
result.append(sums[i]/float(nums[i]))
return result
root = TreeNode(3)
root.left = TreeNode(9)
root.right = TreeNode(20)
root.right.left = TreeNode(15)
root.right.right = TreeNode(7)
assert Solution().averageOfLevels(root) == [3, 14.5, 11]
