java用三种方法实现阶乘n!_JAVA_编程开发_程序员俱乐部

? 用三种方法来实现n!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!.废话不多说,直接上代码:

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? 第一种方法:

?//第一种方法:

package Factorial;

import java.math.BigDecimal;
import java.util.Scanner;
public class Factorial1 {
	public static BigDecimal factorial(int n){ 
		BigDecimal result = new BigDecimal(1);
		BigDecimal a;
		for(int i = 2; i <= n; i++){
			a = new BigDecimal(i);
			result = result.multiply(a);
		}
		return result;
	}
	
	public static void main(String[] arguments){
		Scanner sc = new Scanner(System.in);
		int a = sc.nextInt();
		System.out.println(a + "!=" + factorial(a));
	}

}

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? 第二种方法:

?

?

//第二种方法
package Factorial;

import java.math.BigDecimal;
import java.util.Scanner;
public class Factorial3 {
	public static BigDecimal factorial(BigDecimal n){
		BigDecimal bd1 = new BigDecimal(1);
		BigDecimal bd2 = new BigDecimal(2);
		BigDecimal result = bd1;
		while(n.compareTo(bd1) > 0){
			result = result.multiply(n.multiply(n.subtract(bd1)));
			n = n.subtract(bd2);
		}
		return result;
	}
	public static void main(String[] arguments){
		Scanner sc = new Scanner(System.in);
		BigDecimal  n = sc.nextBigDecimal();
		
		System.out.print(n + "!=" + factorial(n));
	}

}

?第三种方法,用递归实现:

?

?

package Factorial;

import java.util.Scanner;
import java.math.BigDecimal;
public class Factorial2 {
	public static BigDecimal factorial(BigDecimal n){
		BigDecimal bd1 = new BigDecimal(1);
		if(n.equals(new BigDecimal(1))){
			return bd1;
		}
		else
			return n.multiply(factorial(n.subtract(bd1)));
	}
	public static void main(String[] arguments){
		Scanner sc = new Scanner(System.in);
		BigDecimal a = sc.nextBigDecimal();
		BigDecimal result = factorial(a);	
		System.out.println(a + "!=" +result);
		
	}

}

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