每日算法题: Most Frequent Subtree Sum

Hi, here's your problem today. This problem was recently asked by LinkedIn:

Given a binary tree, find the most frequent subtree sum.

Example:

   3

  / \

 1   -3

The above tree has 3 subtrees. The root node with 3, and the 2 leaf nodes, which gives us a total of 3 subtree sums. The root node has a sum of 1 (3 + 1 + -3), the left leaf node has a sum of 1, and the right leaf node has a sum of -3. Therefore the most frequent subtree sum is 1.

If there is a tie between the most frequent sum, you can return any one of them.

Here's some starter code for the problem:

class Node():

  def __init__(self, value, left=None, right=None):

    self.val = value

    self.left = left

    self.right = right



def most_freq_subtree_sum(root):

  # fill this in.



root = Node(3, Node(1), Node(-3))

print(most_freq_subtree_sum(root))

# 1