算法题 Maximum Path Sum in Binary Tree

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

You are given the root of a binary tree. Find the path between 2 nodes that maximizes the sum of all the nodes in the path, and return the sum. The path does not necessarily need to go through the root.

class Node:

  def __init__(self, val):

    self.val = val

    self.left = None

    self.right = None



def maxPathSum(root):

  # Fill this in.



# (* denotes the max path)

#       *10

#       /  \

#     *2   *10

#     / \     \

#   *20  1    -25

#             /  \

#            3    4

root = Node(10)

root.left = Node(2)

root.right = Node(10)

root.left.left = Node(20)

root.left.right = Node(1)

root.right.right = Node(-25)

root.right.right.left = Node(3)

root.right.right.right = Node(4)

print maxPathSum(root)

# 42