Too slow two strings comparer

Question

I have 2 strings for example:

abcabc and bcabca
or
aaaabb and abaaba

I checked that second string is the same or not like first string but shifted. bcabca = ..abca + bc...

Here is code it works but too slow:

using System;

public class TOPSES
{
    static string t1, t2;
    static char[] t1c;
    static char[] t2c;

    static void Main()
    {
        int t;
        t = int.Parse(Console.ReadLine());

        while (t > 0)
        {
            t1 = Console.ReadLine();
            t2 = Console.ReadLine();

            string result = "no";

            t1c = t1.ToCharArray();
            t2c = t2.ToCharArray();

            result = ChangeString(t1c[0], 0);

            Console.WriteLine(result);
            t--;
        }
    }

    public static string ChangeString(char letter, int startIndex)
    {
        int index = t2.IndexOf(letter, startIndex);
        if (index == -1)
            return "no";
        else
        {
            string newString = t2.Remove(0, index);
            newString += t2.Remove(index, t2.Length - index);

            if (t1 != newString)
                return ChangeString(letter, ++index);

            return "yes";
        }
    }
}

---

Question:

How to improve this code to make program faster?
Also it will be nice, if someone could explain what in this code make this 'program' slow.

---

Thanks Leonid for source!

Code look now that:

using System;
using System.Linq;

public class TOPSES
{
    static void Main()
    {
        string t1, t2;
        int t;
        t = int.Parse(Console.ReadLine());

        while (t > 0)
        {
            t1 = Console.ReadLine();
            t2 = Console.ReadLine();

            string result = "no";

            if ((t1 + t1).IndexOf(t2) != -1)
                result = "yes";

            Console.WriteLine(result);
            t--;
        }
    }
}

Answer 1

Less is more! So, here is a shorter/cleaner version (not tested):

namespace MyNamespace
{
    using System;

    public class StringExtension
    {
        public static bool IsRotationOf(this string lhs, string rhs)
        {
            return (lhs.Length == rhs.Length) && (lhs+lhs).Contains(rhs));
        }
    }

    public class TestRotation
    {
        public static int Main(string[] args)
        {
            int numTries = Int32.Parse(Console.ReadLine());
            for (int tryIndex = 0; tryIndex < numTries; ++numTries)
            {
                string lhs = Console.ReadLine();
                string rhs = Console.ReadLine();
                bool isRotation = lhs.IsRotationOf(rhs);
                Console.WriteLine(isRotation ? "yes" : "no");
            }

            return 0;
        }
    }
}