java中怎么实现阶乘,如计算1~100的阶乘

Question

如题所述

Answer 1

使用BigInteger大容量运算类计算100的阶乘
一.一般算法(循环)
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public class Test {
public static void main(String[] args) {
int result = 1;
for (int i = 1; i <= 100; i++) {
result *= i;
}
System.out.println(result);
}
}
public class Test {
public static void main(String[] args) {
int result = 1;
for (int i = 1; i <= 100; i++) {
result *= i;
}
System.out.println(result);
}
}
输出结果为0，因为int无法保存下100的阶乘的结果，100的阶乘的长度至少大于50位，也要大于long,double
二.使用BigInteger大容量运算类
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import java.math.BigInteger;

public class Test {
public static void main(String[] args) {
BigInteger result = new BigInteger("1");//为result赋初始值，为1
for (int i = 1; i <= 100; i++) {
BigInteger num = new BigInteger(String.valueOf(i));
result = result.multiply(num);//调用自乘方法
}
System.out.println(result);//输出结果
System.out.println(String.valueOf(result).length());//输出长度
}
}
import java.math.BigInteger;
public class Test {
public static void main(String[] args) {
BigInteger result = new BigInteger("1");//为result赋初始值，为1
for (int i = 1; i <= 100; i++) {
BigInteger num = new BigInteger(String.valueOf(i));
result = result.multiply(num);//调用自乘方法
}
System.out.println(result);//输出结果
System.out.println(String.valueOf(result).length());//输出长度
}
}
计算结果为：93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
产度:158

Answer 2

Java计算阶乘（n!）需要使用实现使用BigDecimal类,因为用int最多正确算到12!,用long最多正确算到20!
以下是详细代码：
import java.math.BigDecimal;
import java.util.Scanner;
public class Factorial3 {
public static BigDecimal factorial(BigDecimal n){
BigDecimal bd1 = new BigDecimal(1);//BigDecimal类型的1
BigDecimal bd2 = new BigDecimal(2);//BigDecimal类型的2
BigDecimal result = bd1;//结果集，初值取1
while(n.compareTo(bd1) > 0){//参数大于1，进入循环
result = result.multiply(n.multiply(n.subtract(bd1)));//实现result*（n*（n-1））
n = n.subtract(bd2);//n-2后继续
}
return result;
}
public static void main(String[] arguments){
Scanner sc = new Scanner(System.in);
BigDecimal n = sc.nextBigDecimal();

System.out.print(n + "!=" + factorial(n));
}

}

Answer 3

import java.util.Scanner;

public class Jiecheng {
public static void main(String[] args) {
System.out.print("请输入你想要的阶乘数：");
Scanner scan = new Scanner(System.in);
int a = scan.nextInt();
System.out.print("!" + a + "的结果是：" + jiecheng(a));
}

public static double jiecheng(int a) {
if (a <= 1) {
return a;
}

return jiecheng(a - 1) * a;
}

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