[13.1.变量的作用域问题（重点）](13.1.%E5%8F%98%E9%87%8F%E7%9A%84%E4%BD%9C%E7%94%A8%E5%9F%9F%E9%97%AE%E9%A2%98%EF%BC%88%E9%87%8D%E7%82%B9%EF%BC%89.md) [13.2.递归函数/递归思想（重点/难点）](13.2.%E9%80%92%E5%BD%92%E5%87%BD%E6%95%B0-%E9%80%92%E5%BD%92%E6%80%9D%E6%83%B3%EF%BC%88%E9%87%8D%E7%82%B9-%E9%9A%BE%E7%82%B9%EF%BC%89.md)