Binary Tree Level with Minimum Sum

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

You are given the root of a binary tree. Find the level for the binary tree with the minimum sum, and return that value.

For instance, in the example below, the sums of the trees are 10, 2 + 8 = 10, and 4 + 1 + 2 = 7. So, the answer here should be 7.

class Node:

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

    self.val = value

    self.left = left

    self.right = right



def minimum_level_sum(root):

  # Fill this in.



#     10

#    /  \

#   2    8

#  / \    \

# 4   1    2

node = Node(10)

node.left = Node(2)

node.right = Node(8)

node.left.left = Node(4)

node.left.right = Node(1)

node.right.right = Node(2)



print minimum_level_sum(node)