用递归函数求x! x!={1(x=0)x(x−1)!(x>0)x!=\left\{\begin{matrix}1 & & (x=0) \\ x(x-1)! & &(x>0) \end{matrix}\right.x!={1x(x−1)!(x=0)(x>0)
整数x，x不大于12
n!
3!
6
