To a binary tree, find the average of the maximum sub-tree. Returns the root of the subtree.
Example
Sample 1
输入：
{1,-5,11,1,2,4,-2}
输出：11
说明:
这棵树如下所示：
1
/ \
-5 11
/ \ / \
1 2 4 -2
11子树的平均值是4.333，为最大的。
Sample 2
输入：
{1,-5,11}
输出：11
说明:
1
/ \
-5 11
1,-5,11 三棵子树的平均值分别是 2.333,-5,11。因此11才是最大的.
参考代码："""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
class Solution:
"""
@param root: the root of binary tree
@return: the root of the maximum average of subtree
"""
def findSubtree2(self, root):
# write your code here
self._result_node = None
self._result_val = -float("inf")
self.find_sub_tree(root)
return self._result_node
def find_sub_tree(self, root):
if not root:
return 0, 0
left_sum, left_size = self.find_sub_tree(root.left)
right_sum, right_size = self.find_sub_tree(root.right)
sum = root.val + left_sum + right_sum
size = left_size + right_size + 1
avg_val = float(sum)/size
if self._result_node is None or self._result_val < avg_val:
self._result_node = root
self._result_val = avg_val
return sum, size
About when to use the member variables of the problem, if _result_node not a member variable, you need to return a parameter, when used in traversing all the nodes, resulting in code duplication, and therefore more directly member variables (global taste a little).
Official Code: [write better than me, especially the use of static member variables]
class Solution:
# @param {TreeNode} root the root of binary tree
# @return {TreeNode} the root of the maximum average of subtree
average, node = 0, None
def findSubtree2(self, root):
# Write your code here
self.helper(root)
return self.node
def helper(self, root):
if root is None:
return 0, 0
left_sum, left_size = self.helper(root.left)
right_sum, right_size = self.helper(root.right)
sum, size = left_sum + right_sum + root.val, \
left_size + right_size + 1
if self.node is None or sum * 1.0 / size > self.average:
self.node = root
self.average = sum * 1.0 / size
return sum, size