Lucky Number in Java

In this section, we will learn what is a luck number and also create Java programs to check if the given number is a lucky number or not. The lucky number program frequently asked in Java coding tests and academics.

Lucky Number

The sequence of natural numbers or subset of integers that we get after removing second, third, fourth, fifth, and so on number respectively from the sequence. By applying the process there still remains some numbers indefinitely in the sequence such numbers are known as lucky numbers.

Let's understand it through an example.

Lucky Number Example

Consider the sequence of following natural numbers:

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, ….

Let's remove every second number (2, 4, 6, 8, 10, ……) from the above sequence, we get:

1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, …………

Let's remove every third number (5, 11, 17, 23, ……) from the above sequence, we get:

1, 3, 7, 9, 13, 15, 19, 21, 25, …….

Continue the above process indefinitely by removing the fourth, fifth, sixth,……, and so on, until after a fixed number of steps, certain natural numbers remain indefinitely. The numbers that remains in the sequence are known as lucky Numbers.

Algorithm

Begin
   counter := 2 (It is static data, not be initialized again in recursion call)
   if counter > n, then
      return 1
   if n mod counter = 0, then
      return 0
   n := n - (n / counter)
   counter := counter + 1
   isLuckyNumber(n)
End

Let's implement the above steps in a Java program.

Lucky Number Java Program

LuckyNumberExample1.java

import java.util.*;
public class LuckyNumberExample1
{
public static int count = 2;
//function that checks if the given number is lucky or not
//returns 1 if the number is lucky, else returns 0
static boolean isLuckyNumber(int n)
{
if(count > n)
return true;
if(n%count == 0)
return false;	
//determines the position of the given number
n = n-(n/count);
//increments the count variable by 1
count++;
return isLuckyNumber(n);
}
//driver code
public static void main (String args[])
{
Scanner sc=new Scanner(System.in);
System.out.print("Enter the number: "); 
//reads an integer from the user
int num=sc.nextInt();
//calling user-defined function 
if(isLuckyNumber(num))
System.out.println(num+" is a Lucky Number.");
else
System.out.println(num+" is not a Lucky Number.");
}
}

Output 1:

Enter the number: 19
19 is a Lucky Number.

Output 2:

Enter the number: 89
89 is not a Lucky Number.

Let's create another Java program that finds all the lucky numbers for the specified range.

LuckyNumberExample2.java

import java.util.*; 
public class LuckyNumberExample2
{ 
public static void main(String args[])
{
Scanner sc=new Scanner(System.in);
System.out.print("Enter the number of elements: "); 
//reading an integer from the user that represents the number of elements
int n=sc.nextInt();
//creates an array of n
int arr[]=new int[n]; 
//assigning the value of n into elements
int elements=n; 
for(int i=0;i<n;i++) 
{ 
arr[i]=i+1; 
} //end of for loop
int del=1; 
System.out.println("\nLucky Number Operation:\n"); 
while(del<n) 
{ 
for(int i=del; i<n; i+=del) 
{ 
for(int j=i; j<n-1; j++) 
{ 
arr[j]=arr[j+1]; 
} //end of for loop
n--; 
} //end of for loop
del++; 
for(int i=0; i<n; i++) 
{ 
System.out.print(arr[i]+" "); 
} //end of for loop
System.out.println(); 
} //end of while loop
System.out.print("\nHence, the Lucky Numbers Less than "+elements+" are: "); 
for(int i=0; i<n; i++) 
{ 
//prints the lucky numbers
System.out.print(arr[i]+" "); 
} //end of for loop
} 
}

Output: