110. Balanced Binary Tree

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.

题意：问给定的二叉树是不是平衡的二叉树（同属一个节点的子树高度相差不大于1）

代码如下：

/** * Definition for a binary tree node. * function TreeNode(val) { *     this.val = val; *     this.left = this.right = null; * } *//** * @param {TreeNode} root * @return {boolean} */var isBalanced = function(root) {    if(!root) return true;    if(Math.abs(getDepth(root.left)-getDepth(root.right))>1) return false;    return isBalanced(root.left) && isBalanced(root.right);};var getDepth=function(root){    if(!root) return 0;    return 1+Math.max(getDepth(root.left),getDepth(root.right));}