阶乘，递归，方法的运用

求1！+2！+。。。+5！ 如3！=1*2*3

①普通方式

public static void main(String[] args) {
        int sum =0;//定义总和
        int factorialSum  =0 //算第几个数的阶乘 
        for(int i = 1;i<=5;i++){
            factorialSum *=i;
            sum +=factorialSum;
        }
        System.out.println(sum);
}

②方法的运用

class Factorial{
//求第几数的阶乘
int factorialSum（int pnum）{
int sum=1;
for(int i=1;i<=pnum;i++){
sum *=i;
}
return sum;
}
//求和
int add(int pnum){
int sum =0;
for(int i=1;i<=pnum;i++){
sum +=factorialSum(i);
}
return sum;
}
public static void main(String[] args) {
 Factorial m = new  Factorial();
 System.out.println(m.add(5));
}
}

递归方法

class Factorial{
//求第几数的阶乘
int factorialSum（int pnum）{
if(pum==1 || pum==2){
return 1;
}
return pnum*factorialSum(pnum-1);
}
//求和
int add(int pnum){
int sum =0;
for(int i=1;i<=pnum;i++){
sum +=factorialSum(i);
}
return sum;
}
public static void main(String[] args) {
 Factorial m = new  Factorial();
 System.out.println(m.add(5));
}
}