一个c#面试题

C#
给你一个string字符串， abcd as,ccd.dsa
反转这个字符串变为：   dsa.ccd,as abcd

要求：不能用【任何】【系统函数】。

实现代码如下：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;


namespace ReverseString
{
    class Program
    {
        public static string ReverseString(String originalString)
        {
            if (string.IsNullOrWhiteSpace(originalString))
            {
                throw new ArgumentException("orginalString can not be null or white space");
            }
            char[] temp = originalString.ToCharArray();
            int begin = 0, end = temp.Length - 1;
            ReverseCharArray(temp, begin, end);

            Console.WriteLine(temp);

            int i = 0, j = 0;
            int k = 0;
            do
            {
                if (!char.IsLetter(temp[k]))
                {
                    j = k - 1;
                    ReverseCharArray(temp, i, j);
                    i = k + 1;
                }               
                k++;
            }
            while (k <= end);
            if (char.IsLetter(temp[end]))
            {
                ReverseCharArray(temp, i, end);
            }     
            string finalString = new string(temp);
            return finalString;

        }
        public static void ReverseCharArray(char[] charArray, int begin, int end)
        {
            while (begin < end)
            {
                char temp = charArray[begin];
                charArray[begin] = charArray[end];
                charArray[end] = temp;
                begin++;
                end--;
            }
        }

        static void Main(string[] args)
        {
            String originalString = "abcd as,ccd.dsa";
            String ouput = "dsa.ccd,as abcd";
            ReverseString(originalString);
            Console.ReadKey();
        }

    }
}