递归算法

递归算法

The Three Laws of Recursion
A recursive algorithm must have a base case.
A recursive algorithm must change its state and move toward the base case.
A recursive algorithm must call itself, recursively.

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对应三条规则
1 写出初始情况返回值
2 写出操作，= +/- 等等
3 调用自己，并且传递参数，通过不停调用自己，最后能达到初始情况

递归算法不关心具体的实现，只关心具体某一步的实现