欧拉计划 第4题

A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 * 99.

Find the largest palindrome made from the product of two 3-digit numbers.

 

class Program

    {

        static void Main(string[] args)

        {

            /*

             * A palindromic number reads the same both ways. 

             * The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 * 99.

             * Find the largest palindrome made from the product of two 3-digit numbers.

             */



            Console.WriteLine(CheckPalindromicNumber(123));

            Console.WriteLine(CheckPalindromicNumber(121));

            Console.WriteLine(CheckPalindromicNumber(1221));

            Console.WriteLine(CheckPalindromicNumber(12321));



            int k = 1;

            for (int i = 999; i >= 0; i--)

            {

                for (int j = 999; j >= 0; j--)

                {

                    int n = i*j;

                    if (n > k && CheckPalindromicNumber(n))

                    {

                        k = n;

                    }

                }

            }

            Console.WriteLine(k);

        }



        private static bool CheckPalindromicNumber(int n)

        {

            string nString = n.ToString();

            for (int a = 0, b = nString.Length - 1; a < b; a++, b--)

            {

                if (nString[a] != nString[b]) return false;

            }

            return true;

        }



    }