C#中字符压缩和解压缩

 2016/06/30 .牛栏前
 1  static void Main(string[] args)
        {
            string result = "xxxyyyyyyz";
            Console.WriteLine(result);
            Console.WriteLine(ExtractString("9a5b"));           
            Console.ReadLine();
        }

        //StringBuilder在拼接大量字符串的時候相對String來說具有很高的效率，這是
        //由於StringBuilder在內部處理上使用了字符串的鏈式存儲表示法，可設置容量，
        //若超過容量，會重新分配存儲空間

        //壓縮
        public static string CompressString(string str)
        {
            const int iMaxCount = 9;
            StringBuilder stringBuilder = new StringBuilder();
            int countChar = 1;  //計數器
            str = str.Trim() + " "; //防止循環溢出，加上空格

            for (int i = 0; i < str.Length - 1; i++)
            {
                if (str[i + 1] == str[i])//有連續字符
                {
                    countChar++;//計數器加一
                    if (countChar > iMaxCount) //如果大於9,壓入stringBuilder,如a10=a9a1解決二義性(如a101b3的多種理解)
                    {
                        stringBuilder.Append(iMaxCount.ToString());
                        stringBuilder.Append(str[i]);
                        countChar = 1;
                    }
                    continue;
                   // break;
                }
                else  //如果不等，就將當前的字符和計數壓入stringBuilder
                {
                    if (countChar == 1) //如果字符為1則不顯示
                    {          
                        stringBuilder.Append(str[i]);
                        countChar = 1;
                    }
                    else
                    {
                        stringBuilder.Append(countChar.ToString());
                        stringBuilder.Append(str[i]);
                        countChar = 1;
                    }

                }
            }
         
            return stringBuilder.ToString();
        }

        //解壓縮
        private  static string ExtractString(string str)
        {
            int a;
            StringBuilder stringBuilder = new StringBuilder();
            str = str.Trim() + " ";
            for (int i = 0; i < str.Length - 1;i=i+2 )
            {
                a = (int)(str[i])-(int)'0'; //將字符轉換為整型
                for (int j = 0; j < a; j++)
                {
                    stringBuilder.Append(str[i + 1]);
                }
            }
            return stringBuilder.ToString();
        }