【算法基石】二叉树前序、中序、后序、层次、深度优先（前序）、广度优先（层次）遍历

二叉树遍历[C++] https://blog.csdn.net/gatieme/article/details/51163010
二叉树遍历[Java] https://www.cnblogs.com/llguanli/p/7363657.html
二叉树遍历[Python] https://my.oschina.net/magicalee/blog/2209301