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阶乘求和

题目:求1+2!+3!+...+20!的和
方案1
//第i项的阶乘值f(n)=f(n-1)*n
public static int getFactorial(int i){
    if (i==1) {   //第一项为1
       return 1;
    }
    return getFactorial(i-1)*i; //阶乘值=上一个阶乘值*第n项
}

//调用
int sum = 0;
for (int i = 1; i <= 20; i++) {
    System.out.println("第"+i+"项阶乘值为:"+getFactorial(i));
    sum+=getFactorial(i);
}
System.out.println("1+2!+3!+...+20!的和为:"+sum);


方案2
//第二种方法,通过循环计算出每一个阶乘项的值
public static int getFactorial20(){
    int sum = 0;
    int fac = 1;
    for (int i = 1; i <= 20; i++) {    //总共20项
        fac*=i;    //没一项的值
        System.out.println("@方案two"+i+"项阶乘值为:"+fac);
        sum+=fac;
    }
    System.out.println("@方案two1+2!+3!+...+20!的和为:"+sum);
    return sum;
}

源码

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