110-Balanced Binary Tree

Description

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.

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Example 1:

Given the following tree [3,9,20,null,null,15,7]:

3 / \ 9 20 / \ 15 7

Return true.

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Example 2:

Given the following tree [1,2,2,3,3,null,null,4,4]:

1 / \ 2 2 / \ 3 3 / \ 4 4

Return false.

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问题描述

给定一个二叉树， 判断它的高度是否平衡

高度平衡的二叉树定义如下:

每个节点的左右子树的高度的差值的绝对值不会大于1

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问题分析

在后序遍历的过程中求高度并进行判断

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解法

public class Solution { public boolean isBalanced(TreeNode root) { return helper(root) != -1; } private int helper(TreeNode root) { if (root == null) return 0; int left = helper(root.left); int right = helper(root.right); if (left == -1 || right == -1 || Math.abs(left - right) > 1) return -1; return Math.max(left, right) + 1; } }