Tag: Recursion

Emirp Number

AnujLeave a comment

An emirp number is a number which is prime backwards and forwards. Example : 13 and 31 are both prime numbers. Thus 13 is a emirp number.

import java.util.*;
class Emirp
{ 
    int n, rev,f;
    Emirp(int nn)
    {
        n=nn;
        rev=0;
        f=2;
    }
    int isprime(int x)
    {
        if(n==x)
        return 1;
        else if (n%x==0 || n==1)
        return 0;
        else
        return isprime(x+1);
    }
    void isEmirp()
    {
        int x=n;
        while(x!=0)
     {
         rev=rev*10 + x%10;
         x=x/10;
         
        }
        int ans1=isprime(f);
        n=rev;
        f=2;
        int ans2=isprime(f);
        if(ans1==1 && ans2==1)
        System.out.println(n+"is an emirp no");
        else
        System.out.println(n+"is not an emirp no.");
        
    }
    public static void main(String[] args) 
    { 
      int a; 
      Scanner sc= new Scanner(System.in);
      System.out.println("Enter the number:");
      a=sc.nextInt();
        Emirp emp=new Emirp(a);
        emp.isEmirp();

    } 
}

Enter the number:
13
31is an emirp no
Enter the number:
51
15is not an emirp no.

Java program – Factorial using recursion

AnujLeave a comment 

import java.util.*;    
class factRec
{  
        int factorial(int n) //5 ! =5*4*3*2*1 =120 
     {    
      if (n == 0)       // 0!=1 so when given number is 0, it returns 1
        return 1;    
      else          // finding factorial by n * factorial(n-1)
        return(n * factorial(n-1));    
     }    
     public static void main(String args[])
     {  
         Scanner sc=new Scanner(System.in);
         factRec fr=new factRec();   //creating object fr
         System.out.println("Enter the number to find the factorial");
         int number=sc.nextInt();//It is the number to calculate factorial
         int fact=1;  
         fact = fr.factorial(number);   //method invocation factorial(number)
                                        // calling recursive method
         System.out.println("Factorial of "+number+" is: "+fact);    
     }  
    }

Output:

Enter the number to find the factorial
5
Factorial of 5 is: 120
Enter the number to find the factorial
8
Factorial of 8 is: 40320

Recursive method

AnujLeave a comment

Find the output of the following fragment:

public class st
{

static int strange(int x,int y)
{
if(x>=y)
{
x=x-y;
return strange(x,y);
}
else
return x;
}

}

 

dry run

1    x=20,y=5               strange(20,5)

2.  x=15,y=5                strange (15,5)

3. x=10,y=5                strange (10,5)

4. x=5,y=5                   strange(5,5)

5. x=0,y=5                   strange(0,5)

returns  0;