Balanced Binary Tree Leetcode Python

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.

这道题目在CC150上面也有。做法是先定义一个depth 计算每个点的depth.当任意两个leaf 的深度差大于1时候就返回false:

The definition of balanced binary tree is any two leaves depth's difference is not greater than 1. so we need to define a function to recursively find the depth of nodes and then recursively compare the depth. 

the time complexity is O(n)

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param root, a tree node
    # @return a boolean
    def depth(self,root):
        if root==None:
            return 0
        if root.left==None and root.right==None:
            return 1
        if root.left==None:
            return self.depth(root.right)+1
        if root.right==None:
            return self.depth(root.left)+1
        return max(self.depth(root.left),self.depth(root.right))+1
    def isBalanced(self, root):
        if root==None:
            return True
        if abs(self.depth(root.left) - self.depth(root.right))>1:
            return False
        else:
            return self.isBalanced(root.left) and self.isBalanced(root.right)