【LeetCode】 110. Balanced Binary Tree 平衡二叉树（Easy）（JAVA）
题目地址: https://leetcode.com/problems/balanced-binary-tree/
题目描述：
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 left and right subtrees of every node differ in height by no 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
题目大意
给定一个二叉树，判断它是否是高度平衡的二叉树。
本题中，一棵高度平衡二叉树定义为：
一个二叉树每个节点 的左右两个子树的高度差的绝对值不超过1。
解题方法
1、采用递归计算二叉树的高度
2、遇到左右节点高度大于 1 的，直接返回结果
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public boolean isBalanced(TreeNode root) {
int height = height(root);
return height != -1;
}
public int height(TreeNode root) {
if (root == null) return 0;
int left = height(root.left);
if (left == -1) return -1;
int right = height(root.right);
if (right == -1) return -1;
if (Math.abs(left - right) > 1) return -1;
return Math.max(left, right) + 1;
}
}
执行用时 : 1 ms, 在所有 Java 提交中击败了 99.81% 的用户
内存消耗 : 40.2 MB, 在所有 Java 提交中击败了 17.65% 的用户