leetcode 110. balanced Binary Tree

题目

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.

代码

# Definition for a binary tree node.# class TreeNode(object):#     def __init__(self, x):#         self.val = x#         self.left = None#         self.right = Noneclass Solution(object):    def isBalanced(self, root):        """        :type root: TreeNode        :rtype: bool        """        if root == None:            return True        left = self.depth(root.left)        right = self.depth(root.right)        return abs(left-right) <= 1 and self.isBalanced(root.left) and self.isBalanced(root.right)    def depth(self, root):        if root == None:            return 0        return max(self.depth(root.left), self.depth(root.right)) + 1

1.定义一个depth函数，用于计算从当前位置起的depth
2.从根节点开始计算其左子树和右子树分别的depth，iterative，两者差距小于1，并且其左子树和右子树都balance，则其为balance