Largest palindrome which is product of two n-digit numbers

http://www.geeksforgeeks.org/largest-palindrome-product-two-n-digit-numbers/

Given a value n, find out the largest palindrome number which is product of two n digit numbers.

Below are steps to find the required number.
1) Find a lower limit on n digit numbers. For example, for n = 2, lower_limit is 10.
2) Find an upper limit on n digit numbers. For example, for n = 2, upper_limit is 99.
3) Consider all pairs of numbers where ever number lies in range [lower_limit, upper_limit]

int larrgestPalindrome(int n)

{

    int upper_limit = 0;

 

    /* Loop to calculate upper bound(largest number

       of n-digit)*/

    for (int i=1; i<=n; i++)

    {

        upper_limit *= 10;

        upper_limit += 9;

    }

 

    // largest number of n-1 digit. One plus this number

    // is lower limit which is product of two numbers.

    int lower_limit = 1 + upper_limit/10;

 

    int max_product = 0; // Initialize result

    for (int i=upper_limit; i>=lower_limit; i--)

    {

        for (int j=i; j>=lower_limit; j--)

        {

            // calculating product of two n-digit numbers

            int product = i * j;

            if (product < max_product)

                break;

            int number = product;

            int reverse = 0;

 

            /* calculating reverse of product to check

               whether it is palindrome or not*/

            while (number != 0)

            {

                reverse = reverse * 10 + number % 10;

                number /= 10;

            }

 

            /* update new product if exist and if

               greater than previous one*/

            if (product == reverse && product > max_product)

                max_product = product;

        }

    }

    return max_product;

}




http://www.geeksforgeeks.org/largest-palindrome-product-two-n-digit-numbers/