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93. 平衡二叉树
给定一个二叉树,确定它是高度平衡的。对于这个问题,一棵高度平衡的二叉树的定义是:一棵二叉树中每个节点的两个子树的深度相差不会超过1。
样例
给出二叉树 A={3,9,20,#,#,15,7}
, B={3,#,20,15,7}
A) 3 B) 3 / \ \ 9 20 20 / \ / \ 15 7 15 7
二叉树A是高度平衡的二叉树,但是B不是
"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
class Solution:
"""
@param root: The root of binary tree.
@return: True if this Binary tree is Balanced, or false.
"""
def isBalanced(self, root):
# write your code here
isBalanced_, _ = self.dfs(root)
return isBalanced_
def dfs(self, root):
if root is None:
return True, 0
isleftBalanced, leftH = self.dfs(root.left)
isrightBalanced, rightH = self.dfs(root.right)
if not isleftBalanced or not isrightBalanced:
return False, 0
return abs(leftH - rightH) <= 1, max(leftH, rightH) + 1