【算法初步】编写一个递归的静态方法计算ln(N!)的值

//直接使用Math库
public static double log(double a)

Returns the natural logarithm (base e) of a double value. Special cases:

• If the argument is NaN or less than zero, then the result is NaN.
• If the argument is positive infinity, then the result is positive infinity.
• If the argument is positive zero or negative zero, then the result is negative infinity.

The computed result must be within 1 ulp of the exact result. Results must be semi-monotonic.

Parameters:

a - a value

Returns:

the value ln a, the natural logarithm of a.

public static double logN(double N)
	{
		if(N == 0 || N == 1)return 0.0;  // 0的阶乘和1的阶乘都为1
		else {
			return Math.log(N)+logN(N-1);
		}
		
	}