110._balanced_binary_tree.md

110. Balanced Binary Tree

难度: 简单

刷题内容

原题连接

• https://leetcode.com/problems/balanced-binary-tree

内容描述

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.

解题方案

思路 1

递归,判断左右子树最大高度差不超过1且左右子树均为平衡树

class Solution(object):
    def isBalanced(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        def height(node):
            if not node:
                return 0
            return 1 + max(height(node.left), height(node.right))
        if not root:
            return True
        return abs(height(root.left) - height(root.right)) <= 1 and self.isBalanced(root.left) and self.isBalanced(root.right)