Given the root of a tree, you are asked to find the most frequent subtree sum. The subtree sum of a node is defined as the sum of all the node values formed by the subtree rooted at that node (including the node itself). So what is the most frequent subtree sum value? If there is a tie, return all the values with the highest frequency in any order.
Examples 1
- Input:
5
/
2 -3
- return [2, -3, 4], since all the values happen only once, return all of them in any order.
Examples 2
- Input:
5
/
2 -5
- return [2], since 2 happens twice, however -5 only occur once.
Note:
- You may assume the sum of values in any subtree is in the range of 32-bit signed integer.
Python Solution:
# 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 findFrequentTreeSum(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root: return []
def postorder(root, d):
cur = root.val
if root.left:
cur += postorder(root.left, d)
if root.right:
cur += postorder(root.right, d)
d[cur] += 1
return cur
d = collections.defaultdict(int)
postorder(root, d)
max_sum = max(d.values())
return [val for val in d if d[val] == max_sum]
OR
# 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 findFrequentTreeSum(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root: return []
def postorder(root, d):
if not root: return 0
cur = root.val
cur += postorder(root.left, d)
cur += postorder(root.right, d)
d[cur] += 1
return cur
d = collections.defaultdict(int)
postorder(root, d)
max_sum = max(d.values())
return [val for val in d if d[val] == max_sum]
OR
# 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 findFrequentTreeSum(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
if not root: return []
d = collections.defaultdict(int)
def recu(root):
if not root: return 0
left = recu(root.left)
right = recu(root.right)
sum = left + right + root.val
d[sum] += 1
return sum
recu(root)
freq = max(d.values())
return [key for key in d if d[key] == freq]
Summary:
- not sure which one is better
LeetCode: 508. Most Frequent Subtree Sum
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