JAVA sum of the two numbers is the reverse of the product error

Question

I'm a beginner to JAVA. I have this school problem: Lisa is hosting a party, during which she has planned for surprise gifts for her guests.

The guests while entering the hall should pick two slips of paper upon which numbers are written.

At the end of the party, the guests should bring their slip of papers to Lisa. The Lucky ones are those who received numbers that satisfy the following condition.

The sum of the two numbers is the reverse of the product of the two numbers.

For example, If a guest has got X and Y as the two numbers, he will be a winner only if

X+ Y= AB; Then X * Y =BA.

Note : Both X and Y should be greater than 0. Otherwise print "Invalid Input"

Sample input 1

24

3

Sample output 1

You are Lucky! Here Is your Gift.

Sample input 2

46

2

Sample output 2

Better Luck Next Time

Sample input 3

0

Sample output 3

Invalid Input

Sample input 4

89

0

Sample output 4

Invalid Input

Code I wrote:

        if(num1>0) 
        {
         System.out.print("Enter second number: ");
         int num2=sc.nextInt();

         if(num2<=0)
         System.out.print("Invalid Input");
         else
           {
            sum=num1+num2;
            product=num1*num2;

            i=product%10;
            product=product/10;
            revproduct=(i*10)+product; 

             if(sum==revproduct)
             System.out.print("You are Lucky! Here Is your Gift."); 
             else
             System.out.print("Better Luck Next Time");
            }      
       else
       System.out.print("Invalid Input");
     }

Error: One test case failed. Same sum and product check

@HimanshuAhuja No, I only tried a combination of inputs that have two digit sum and product. — zeus, Apr 20 '20 at 19:25
That's your problem. E.g. `2 + 497 = 499 <-> 994 = 2 * 497` or `11 + 110 = 0121 <-> 1210 = 11 * 110` --- Or how about single-digit? `2 + 2 = 4 <-> 4 = 2 * 2` or `9 + 9 = 18 <-> 81 = 9 * 9` — Andreas, Apr 20 '20 at 19:27
What test case failed? (`product >= 100`?;) ...your `revproduct` looks ok but works only for 1-99 (max 2 digits)!? — xerx593, Apr 20 '20 at 19:29
@xerx593 `revproduct` only works for 10-99 (exactly 2 digits)! — Andreas, Apr 20 '20 at 19:31
@xerx593 the compiler doesn't mention the failed test case. It just displays: One test case failed. Same sum and product check. — zeus, Apr 20 '20 at 19:32
@zeus You do a web search for [`how to reverse a number`](https://www.google.com/search?q=how+to+reverse+a+number) — Andreas, Apr 20 '20 at 19:34
@xerx593 yes I get it, revproduct works for 2 digits only. Should I use a loop to extend it's range or better approach? — zeus, Apr 20 '20 at 19:35
https://stackoverflow.com/questions/3806126/java-reverse-an-int-value-without-using-array ;) (2nd answer my favourite...yes, you'd do it in a loop) — xerx593, Apr 20 '20 at 19:36
https://stackoverflow.com/questions/3806126/java-reverse-an-int-value-without-using-array — leo, Apr 21 '20 at 07:59
You need to modify **revproduct** function https://stackoverflow.com/questions/3806126/java-reverse-an-int-value-without-using-array — leo, Apr 21 '20 at 08:04

score 1 · Accepted Answer · answered Apr 21 '20 at 08:08

1

while (input != 0) 
{    
    last_digit = input % 10;
    if (last_digit % 2 != 0) {     
        reversedNum = reversedNum * 10 + last_digit;

    }
    input = input / 10; 
}

answered Apr 21 '20 at 08:08

leo

46
5

score 0 · Answer 2 · edited May 03 '20 at 14:30

class Main
{
    public static int reverse(int n)
    {
        int reverse = 0;
        while (n != 0)
        {
            reverse = reverse * 10;
            reverse = reverse + n % 10;
            n = n / 10;
        }
        return reverse;
    }

    public static void main(String args[])
    {
        Scanner sc = new Scanner(System.in);
        int a, b;
        a = sc.nextInt();
        if (a <= 0)
        {
            System.out.println("Invalid Input");
        } else
        {

            b = sc.nextInt();

            if (b <= 0)
            {
                System.out.println("Invalid Input");
            } else
            {
                if (a + b == reverse(a * b))
                {
                    System.out.println("You are Lucky! Here Is your Gift");
                } else
                {
                    System.out.println("Better Luck Next Time");
                }
            }
        }
    }
}

JAVA sum of the two numbers is the reverse of the product error

2 Answers2