平衡二叉树link

<a href="https://baike.baidu.com/item/%E5%B9%B3%E8%A1%A1%E4%BA%8C%E5%8F%89%E6%A0%91/10421057?fr=aladdin" target="_blank">https://baike.baidu.com/item/%E5%B9%B3%E8%A1%A1%E4%BA%8C%E5%8F%89%E6%A0%91/10421057?fr=aladdin</a>

<a href="https://www.cnblogs.com/huangxincheng/archive/2012/07/22/2603956.html" target="_blank">https://www.cnblogs.com/huangxincheng/archive/2012/07/22/2603956.html</a>

<a target="_blank"> http://blog.csdn.net/programmingring/article/details/37969745</a>