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 = None

class 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