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按给定的阶乘数求数

java

-2

Vivek Modi · 技术社区 · 6 年前

我需要根据给定的阶乘数求数。我知道如何求一个数的阶乘,但却坚持要求给定阶乘的数。。

class Fact{  
 public static void main(String args[]){  
  int i,fact=1;  
  int number=5;  
  for(i=1;i<=number;i++){    
      fact=fact*i;    
  }    
  int yo = number(number);
  System.out.println(fact + " " + yo );   

 }  

  public static int number(int no){
      for(int i = 1 ; i >= no ; i--){
          no = no / i;
      }
      return no;
  }
}

0 回复 | 直到 6 年前

Matthew I. 6 年前

我正确理解您的目标,下面是您要查找的代码:

class Fact {

    public static void main(String args[]) {
        int n = 5;

        int fact = factorial(n);
        int number = number(fact);

        System.out.println(n + " "+fact + " " + number);
    }

    public static int factorial(int n) {
        int fact = 1;
        for (int i = 1; i <= n; i++) {
            fact = fact * i;
        }
        return fact;
    }

    public static int number(int factorial) {
        int i = 0;
        do {
            i++;
            factorial = factorial / i;
        } while (factorial > 1);
        return i;
    }
}

输出:

5 120 5

P、 S.功能 number n! = 1 bc这个函数有两个可能的结果-0,1(见这里的结果表 https://en.wikipedia.org/wiki/Factorial n >= 14 由于整数溢出。 数 只为传递的阶乘返回正确的数字。

forpas 6 年前

这种方法:

public static int number(int factorial) {
    if (factorial <= 0) return -1;
    if ((factorial == 1) || (factorial == 2)) return factorial;
    if (factorial % 2 != 0) return -1;

    int i = 1;
    int prod = 1;
    while (prod < factorial) {
        prod *= ++i;
    }
    return (prod == factorial) ? i : -1;
}

以整数作为参数 factorial 并检查它是否是整数的阶乘并返回该整数。
仅限于 12! int 数据类型)
为 1 作为它返回的参数 1 而不是 0 这也是一个解决方案,因为 0! = 1 .
-1 如果不是整数的阶乘。
所以,这个:

public static void main(String[] args) {
    for (int i = -1; i <= 1_000_000_000; i++) {
        int x = number(i);
        if (x > 0)
            System.out.println("Number = " + i + " is the factorial of " + x);
    }
}

将打印:

Number = 1 is the factorial of 1
Number = 2 is the factorial of 2
Number = 6 is the factorial of 3
Number = 24 is the factorial of 4
Number = 120 is the factorial of 5
Number = 720 is the factorial of 6
Number = 5040 is the factorial of 7
Number = 40320 is the factorial of 8
Number = 362880 is the factorial of 9
Number = 3628800 is the factorial of 10
Number = 39916800 is the factorial of 11
Number = 479001600 is the factorial of 12

我不确定这是否是最有效的方法,但它给出了正确的结果。

Madhumitha Kolkar 5 年前

    import java.util.Scanner;

    public class FindNumber{
        public static void main(String args[]){
            int num,fact=1,i;
            Scanner sc = new Scanner(System.in);

            num = sc.nextInt();
            if(num<=0){
                System.out.println("Invalid Input");
                System.exit(0);
            }

            if(num==1){
                System.out.println("1");
                System.exit(0);
            }
if(num==2){
System.out.println("2");
System.exit(0);
}

            for(i=1;i<=num/2;i++){
                fact = fact*i;

                if(fact==num){
                    System.out.println(""+i);
                    System.exit(0);
                }
            }
            System.out.println("Sorry. The given number is not a perfect factorial");
        }
    }