Balanced Binary Tree

每日一题；

今天做的是判断二叉树是否平衡，自己有点没太弄明白概念，所以错了好多次，最后学习了一下别人怎么做的，才做了出来。

1、二叉树平衡是子树的最大深度减去最小深度不超过1；并不是从整棵树来看的，比如说{1,2,2,3,3，#，#，4,4}就是平衡的，但是{1,2,2,3,3,3,3，4,4,4,4,4,4，#，#，5,5}就不是平衡的，画出来才知道啊~

2、做减法的时候要加上绝对值；

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 ofevery node never differ by more than 1.

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public static boolean isBalanced(TreeNode root) {        if(root == null){            return true;        }        if(Math.abs(deepth(root.left) - deepth(root.right))>1){            return false;        }        return isBalanced(root.left) && isBalanced(root.right);    }    public static int deepth(TreeNode root) {        TreeNode treeNode = root;        if(treeNode == null){            return 0;        }        return Math.max(deepth(root.left),deepth(root.right))+1;    }}