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.
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.
思路
任意一个节点的左右子树深度差大于1就返回False，用一个全局变量balance表示返回值。用递归找到每个节点左右子树的深度，如果两者差大于1就将balance置为False。
python代码
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def depth(self, node):
if node == None:
return 0
left = self.depth(node.left) # 左子树深度
right = self.depth(node.right) # 右子树深度
if abs(left - right) > 1:
self.balance = False
return max(left, right) + 1 # 当前节点的深度为左右子树的深度最大值+1
def isBalanced(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
self.balance = True
self.depth(root)
return self.balance
