C# 反转字符串

        static string ReverseString(string str)
        {
            if (str == null || str.Length <= 1)
            {
                return str;
            }
            string result = "";
            for (int i = str.Length - 1; i >= 0; i--)
            {
                result += str[i];
            }
            return result;
        }
 
        static string ReverseString2(string str)
        {
            if (str == null || str.Length <= 1)
            {
                return str;
            }
            StringBuilder sb = new StringBuilder();
            for (int i = str.Length - 1; i >= 0; i--)
            {
                sb.Append(str[i]);
            }
            return sb.ToString();
        }
        static string ReverseString3(string str)
        {
            if (str == null || str.Length <= 1)
            {
                return str;
            }
            char[] charArray = str.ToCharArray();
            for (int i = 0; i < charArray.Length / 2; i++)
            {
                char temp = charArray[i];
                charArray[i] = charArray[charArray.Length - i - 1];
                charArray[charArray.Length - i - 1] = temp;
            }
            return new string(charArray);
        }