Quickest Method to Reverse in String in C#.net

Question

I\'m currently writing a quick solution for Euler Problem #4 where one must find the largest palindromic number from the product of two 3-digit numbers.

To identify if a

Answer 1

Using ggf31416's FastReverse function, here is the solution to Project Euler's Problem #4 which completes on my computer in 47ms.

using System;
using System.Diagnostics;

namespace Euler_Problem_4
{
    class Program
    {
        static void Main(string[] args)
        {
            Stopwatch s = new Stopwatch();
            s.Start();

            int t = 0;

            for (int i = 999; i > 99; i--)
            {
                for (int j = i; j > 99; j--)
                {
                    if (i*j == FastReverse(i*j))
                    {
                        if (i * j > t)
                        {
                            t = i * j;
                        }
                    }
                }
            }

            Console.WriteLine(t);

            s.Stop();
            Console.WriteLine("{0}mins {1}secs {2}ms", s.Elapsed.Minutes, s.Elapsed.Seconds, s.Elapsed.Milliseconds);
            Console.ReadKey(true);

        }

        private static int FastReverse(int num)
        {
            int res = 0;
            int q = (int)((214748365L * num) >> 31);
            int rm = num - 10 * q;
            num = q;
            if (rm == 0) return -1;
            res = res * 10 + rm;
            while (num > 0)
            {
                q = (int)((214748365L * num) >> 31);
                rm = num - 10 * q;
                num = q;
                res = res * 10 + rm;
            }
            return res;
        }
    }
}