Luhna

// Luhn algorithm
import java.io.*;
 
public class GFG {
     

static boolean checkLuhn(String cardNo)
{
    int nDigits = cardNo.length();
 
    int nSum = 0;
    boolean isSecond = false;
    for (int i = nDigits - 1; i >= 0; i--)
    {
 
        int d = cardNo.charAt(i) - '0';
 
        if (isSecond == true)
            d = d * 2;
 
        nSum += d / 10;
        nSum += d % 10;
 
        isSecond = !isSecond;
    }
    return (nSum % 10 == 0);
}
 
 
    static public void main (String[] args)
    {



        String cardNo = "1234567";
        if (checkLuhn(cardNo))
            System.out.println("This is a valid card");
        else
            System.out.println("This is not a valid card");
     
    }
}