Question

I’m trying some online problems. I programmed how to solve the greatest palindrome product of 2 two-digit numbers. For example 91*99=9009. I managed to do it by using the recursive function but I wonder how can i do it using arrays like this one?

product[0]=9;
product[1]=0;
product[2]=0;
product[3]=9;

or if the computed product is 969;

product[0]=9;
product[1]=6;
product[2]=9;

Then I will output it starting from the last index to the first index then test if its equal to the original number.

EDIT:
My question is, how can i store the computed product to an array?

Answer 1

There’s no reason to solve that Project Euler problem using arrays. But if you’re fixated on it, then there is a simple algorithm to convert an array of digits into a number. Just do this:

int number = 0;
int number_2 = 0;

//going forwards:
for (int i = 0; i < array.length; i++)
{
    number = number * 10 + array[i];
}

//going backwards:
for (int i = array.length - 1; i >= 0; i--)
{
    number_2 = number_2 * 10 + array[i];
}

if (number == number_2)
{
    //you have a palindrome
}

It’s not the most efficient method, I know (@Nandkumar’s is faster), but it’s really really simple, that’s what I was aiming for.