Co-Primes in Java

In this tutorial, we will learn to distinguish co-primes from non-co-primes and implement it in Java.
So what exactly are Co-Primes?

Co-Primes

When two numbers have no common factor except “1” then such a pair of numbers are called as Co-primes.
Hence in simple words, if the HCF of the two numbers is 1, then they are called as Co-primes.
Co-primes are also called as Relatively Prime or Mutually Prime.

Note: These two numbers may or may not be prime

Explanation of Co-Primes or not with example

Example 1:

Let number1: 5
Let number2: 50
Factors of number1 are: 1, 5
Factors of number2 are: 1, 2, 5, 10, 25, 50
HCF is 5
Hence they are Not Co-Primes.

Example 2:

Let number1: 14
Let number2: 15
Factors of number1 are: 1, 2, 7, 14
Factors of number2 are: 1, 3, 5, 15
HCF is 1
Hence they are Co-Primes.

Code for Finding Co-Primes or not in Java

import java.util.*;
class coprimes
{
  public static void main(String[]args)
  {
    Scanner scan = new Scanner(System.in);

    System.out.print("Enter number 1: ");
    int num1 = scan.nextInt();
    ArrayList<Integer> arr1 = new ArrayList<Integer>();
    
    System.out.print("Enter number 2: ");
    int num2 = scan.nextInt();
    ArrayList<Integer> arr2 = new ArrayList<Integer>();
    
    for(int i = 0, j = 2; i < num1 ; i++, j++)
    {
      if(num1 % j == 0)  // for finding factors
      {
        arr1.add(j); //storing the factors in a list
      }
    }

    for(int i = 0, j = 2; i < num2; i++, j++)
    {
      if(num2 % j == 0)
      {
        arr2.add(j);
      }
    }

    if(num2 > num1)
    {
      arr2.retainAll(arr1);   //retains all the common elements in both the lists in arr2
      boolean isEqual = arr1.equals(arr2);
      if(isEqual)
      {
        System.out.println("Not Co-Primes");
      }
      else
      {
        System.out.println("Co-Primes");

      }
    }
    else
    {
      arr1.retainAll(arr2);   //retains all the common elements in both the lists in arr1
      boolean isEqual = arr1.equals(arr2);
      if(isEqual)
      {
        System.out.println("Not Co-Primes");
      }
      else
      {
        System.out.println("Co-Primes");

      }
    }	
  }
}

Output:

Enter number 1: 2
Enter number 2: 3
Co-Primes

Hope you’ve understood the code 🙂
Any questions feel free to drop in your comments

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