递归算法：是一种直接或者间接地调用自身的算法。在计算机编写程序中，递归算法对解决一大类问题是十分有效的，它往往使算法的描述简洁而且易于理解。-Recursive algorithm: a call directly or indirectly, its own algorithm. In computer programming, a recursive algorithm to solve a large class of problems is very effective, it is o