【leetcode】【110】Balanced Binary Tree

一、问题描述

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.

二、问题分析

左右子树的高度差超过1就false。显然需要求树的高度，结合之前求过的数的最大和最小高度的方法，稍微修改一下就行了。

三、Java AC代码

public boolean isBalanced(TreeNode root) {
if (root == null)
return true;

if (getHeight(root) == -1)
return false;

return true;
}

public int getHeight(TreeNode root) {
if (root == null)
return 0;

int leftHeight = getHeight(root.left);
int rightHeight = getHeight(root.right);

if (leftHeight == -1 || rightHeight == -1)
return -1;

if (Math.abs(leftHeight - rightHeight) > 1) {
return -1;
}

return Math.max(leftHeight, rightHeight) + 1;

}