蓝桥杯——分而治之的子集数

public class Main{

public static void main(String[] args) {
// TODO Auto-generated method stub
System.out.print(cal(3, 2));
}

static int cal(int n,int m)
{
if(m==0||m>n)
{
return 0;
}
if(m==1||n==m)
{
return 1;
}
return m*cal(n-1, m)+cal(n-1, m-1);
}
}