学步园

public static string ReverseByStack(this string original)
{
    Stack<char> stack = new Stack<char>();
    foreach (char ch in original)
    {
        stack.Push(ch);
    }
    char[] c = new char[original.Length];
    for (int i = 0; i < original.Length; i++)
    {
        c[i] = stack.Pop();
    }
    return new string(c);
}

public static string ReverseByXor(this string original)
{
    char[] charArray = original.ToCharArray();
    int l = original.Length - 1;
    for (int i = 0; i < l; i++, l--)
    {
        charArray[i] ^= charArray[l];
        charArray[l] ^= charArray[i];
        charArray[i] ^= charArray[l];
    }
    return new string(charArray);
}

public static unsafe string ReverseByPointer(this string original)
{
    fixed (char* pText = original)
    {
        char* pStart = pText;
        char* pEnd = pText + original.Length - 1;
        for (int i = original.Length / 2; i >= 0; i--)
        {
            char temp = *pStart;
            *pStart++ = *pEnd;
            *pEnd-- = temp;
        }

        return original;
    }
}