这个题怎么写？大佬们帮帮忙

java计算sum=1-1/2!+1/3!-...(-1)的（n-1）次方1/n!

public class Question
{
    // 计算sum=1-1/2!+1/3!-...(-1)的（n-1）次方1/n!
    public calculate(int n)
    {
        int sign = 1;
        double factorial = 1;
        double sum = 1;
        
        for (int i = 2; i <= n; ++i)
        {
            sign *= -1;
            factorial *= i;
            sum += sign * 1.0 / factorial;
        }
        
        return sum;
    }

}

代码如下，如有帮助，请采纳一下，谢谢。

//计算阶乘
long jiecheng(int n)
{
	if(n <= 0)
		return 1;
	long ll = 1L;
	for (int i = 1; i <= n;i++)
	{
		ll *= i;
	}
	return ll;
}

float fuc(int n)
{
	float sum = 0.000;
	for (int i = 1; i <= n; i++)
	{
		if(i%2 == 0)
			sum = sum + 1/jiecheng(i);
		else
			sum = sum - 1/jiecheng(i);
	}
	return sum;
}