C# 反转句子

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

namespace ReverseSentence
{
    class Program
    {
        static string ReverseSentence(string str)
        {
            if (str == null || str == string.Empty)
            {
                throw new Exception("input string is empty.");
            }

            if (str.Length <= 1)
            {
                return str;
            }

            string[] strArray = SplitWord(str);
            string temp = "";
            string result = "";
            for (int i = 0; i < strArray.Length / 2; i++)
            {
                temp = strArray[i];
                strArray[i] = strArray[strArray.Length - i - 1];
                strArray[strArray.Length - i - 1] = temp;
            }
            foreach (string item in strArray)
            {
                result += item;
            }
            return result;
        }

        static string[] SplitWord(string str)
        {
            int count = 1;
            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] == ' ' || str[i] == ',' || str[i] == '.' || str[i] == '!')
                {
                    count++;
                    count++;
                }
            }

            string[] strArray = new string[count];
            int j = 0;
            for (int i = 0; i < str.Length; i++)
            {
                if (str[i] != ' ' && str[i] != ',' && str[i] != '.' && str[i] != '!')
                {
                    strArray[j] += str[i];
                }
                else
                {
                    j++;
                    strArray[j] += str[i];
                    j++;
                }
            }
            return strArray;
        }

        static string ReverseSentence2(string sentence)
        {
            if (sentence == null || sentence == string.Empty)
            {
                throw new Exception("Input is null.");
            }

            if (sentence.Length <= 1)
            {
                return sentence;
            }

            char[] reverseString = new char[sentence.Length];
            for (int i = 0; i < sentence.Length; i++)
            {
                reverseString[i] = sentence[sentence.Length - i - 1];
            }

            int index = 0;
            int start = 0;
            int length = 0;
            string result = "";
            while (index < reverseString.Length)
            {
                while (index < reverseString.Length)
                {
                    if (reverseString[index] >= 65 && reverseString[index] <= 122)
                    {
                        index++;
                        length++;
                    }
                    else
                    {
                        if (length == 0)
                        {
                            result += reverseString[index];
                            start++;
                            index++;
                        }
                        break;
                    }
                }

                if (length > 0)
                {
                    char[] word = new char[length];
                    for (int i = 0; i < length; i++)
                    {
                        word[i] = reverseString[start + length - i - 1];
                    }
                    for (int j = 0; j < length; j++)
                    {
                        result += word[j];
                    }
                    start += length;
                    length = 0;
                }
            }
            return result;
        }

        static string ReverseSentence3(string str)
        {
            if (str == null || str.Length == 0)
            {
                throw new Exception("input can't be null");
            }

            string rStr = ReverseString(str, 0, str.Length - 1);

            int start = 0;
            int end = 0;
            string result = "";

            for (int i = 0; i < rStr.Length; i++)
            {
                if (rStr[i]== ' ' || rStr[i] == ',' || rStr[i] == '.' || rStr[i]== '!')
                {
                    result += ReverseString(rStr, start, end -1);
                    result += rStr[i];
                    end++;
                    start = end;
                }
                else
                {
                    end++;
                }
            }
            result += ReverseString(rStr, start, end - 1);
            return result;

        }
        static string ReverseString(string str, int start, int end)
        {
            string result = "";
            for (int i = end; i >= start ; i--)
            {
                result += str[i];
            }
            return result;
        }


        static void Main(string[] args)
        {
            string str = Console.ReadLine();
            string result = ReverseSentence2(str);
            Console.WriteLine(result);
        }
    }
}