Question

java： 用递归和非递归两种写出N!写1+1/2-1/3+1/4-1/5……+1/n程序

Answer 1

public class Digui {
//递归算法:
public static double digui(int n){
double sum = 0.0;
if (n == 1) {
sum = 1;
}else{
if (n%2 == 0) {
sum = 1.0/n+digui(n-1);
}else{
sum = -1.0/n+digui(n-1);
}
}
return sum;
}
//非递归算法：
public static double feidigui(int n){
double count = 0.0;
StringBuffer sb = new StringBuffer();
for (double i = 1; i <= n; i++) {
if (i == 1) {
count = 1;
sb.append("n!="+n+"!=1");
}else{
if (i%2 == 0) {
count = count+1/i;
sb.append("+1/"+(int)i);
}else{
count = count-1/i;
sb.append("-1/"+(int)i);
}
}
}
System.err.println(sb.toString());
return count;
}

public static void main(String[] args) {
int n = 10;
double digui = feidigui(n);
double feidigui = digui(n);
System.out.println("递归算法："+n+"! = "+digui);
System.out.println("非递归算法："+n+"! = "+feidigui);
}
}

运行结果如下：
n!=10!=1+1/2-1/3+1/4-1/5+1/6-1/7+1/8-1/9+1/10
递归算法：10! = 1.3543650793650797
非递归算法：10! = 1.3543650793650797