Balanced Binary Tree.py

'''
Given a binary tree, determine if it is height-balanced.

For this problem, a height-balanced binary tree is defined as:

a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example 1:

Given the following tree [3,9,20,null,null,15,7]:

    3
   / \
  9  20
    /  \
   15   7
Return true.

Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

       1
      / \
     2   2
    / \
   3   3
  / \
 4   4
Return false.
'''

# 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 isBalanced(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        return self.search(root)[0]
    
    def search(self, node):
        if not node:
            return True, 0
        left = self.search(node.left)
        right = self.search(node.right)
        if left[0] and right[0] and abs(left[1] - right[1]) < 2:
            return True, max(left[1], right[1]) + 1
        else:
            return False, max(left[1], right[1]) + 1