平衡二叉树

特性：
它是一棵空树或它的左右两个子树的高度差的绝对值不超过1，并且左右两个子树都是一棵平衡二叉树，同时，平衡二叉树必定是二叉搜索树，反之则不一定。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace BalanceTree
{
    public class TreeNode
    {
        public int value;
        public TreeNode left;
        public TreeNode right;

        TreeNode(int x)
        {
            value = x;
        }

    }

    class Program
    {
        public bool isBalance(TreeNode root)
        {
            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;
        }

        static void Main(string[] args)
        {
           
        }
    }
}