关于老赵微博得一道题的解法

给出一种解决方案如下：
 internal class ConvertTool
    {
        static Random mRad = new Random();
        const int ConvertMinLength = 4;
        private static char[] SplitChars = new[] { ' ', ',', '.', '!' };

        /// <summary>
        /// 转换
        /// </summary>
        /// <param name="textString"></param>
        /// <returns></returns>
        public static string ConverText(string textString)
        {
            int textLength = textString.Length;
            var firstSplitCharIndex = textString.IndexOfAny(SplitChars);
            if (firstSplitCharIndex < ConvertMinLength)
            {
                return textString;
            }

            StringBuilder stringBuilder = new StringBuilder(textString);
            int startRandomIndex = 1;
            const int randomStep = 2;
            var splitCharIndex = firstSplitCharIndex;
            while (splitCharIndex != -1 && splitCharIndex < textLength)
            {
                ConvertWordToRandom(stringBuilder, startRandomIndex, splitCharIndex - randomStep);
                startRandomIndex = splitCharIndex + randomStep;
                splitCharIndex = textString.IndexOfAny(SplitChars, splitCharIndex + 1);
                Console.WriteLine("splitCharIndex-{0},startRandomIndex-{1}", splitCharIndex, startRandomIndex);
            }
            return stringBuilder.ToString();
        }

        /// <summary>
        /// 打乱某个单词
        /// </summary>
        /// <param name="sb"></param>
        /// <param name="startIndex"></param>
        /// <param name="endIndex"></param>
        static void ConvertWordToRandom(StringBuilder sb, int startIndex, int endIndex)
        {
            if (startIndex >= endIndex)
            {
                return;
            }

            var sourceIndex = startIndex;
            var validateLength = endIndex - startIndex;
            while (validateLength > 1)
            {
                var targetIndex = mRad.Next(validateLength) + sourceIndex;
                SwitchToChar(sb, sourceIndex, targetIndex);
                sourceIndex++;
                validateLength = endIndex - sourceIndex;
            }
        }

        /// <summary>
        /// 替换指定两个位置的字符
        /// </summary>
        /// <param name="sb"></param>
        /// <param name="sourceIndex"></param>
        /// <param name="targetIndex"></param>
        private static void SwitchToChar(StringBuilder sb, int sourceIndex, int targetIndex)
        {
            if (sourceIndex == targetIndex || sourceIndex < 0 || sourceIndex >= sb.Length || targetIndex < 0 || targetIndex >= sb.Length)
            {
                return;
            }
            char tempChar = sb[targetIndex];
            sb[targetIndex] = sb[sourceIndex];
            sb[sourceIndex] = tempChar;
        }
    }