using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string str = "My Name is khan. What's is your name?";

        Console.WriteLine(ReverseWord(str));

        Console.WriteLine(ReverseAWordUsingStack(str));

    }

    public static string ReverseWord(string str)

    {

        int lastIndex = 0;

        for(var i=0; i < str.Length; i++)

        {

            if(str[i]==' ')

            {

                str = Reverse(str, lastIndex, i-1);

                lastIndex = i + 1;

            }

        }

        str = Reverse(str, lastIndex, str.Length-1);

        str = Reverse(str, 0, str.Length-1);

        return str;     

    }

    public static string Reverse(string str, int startIndex, int endIndex){

        char[] strChar = str.ToCharArray();

        char tempChar;

        while(startIndex < endIndex)

        {

            tempChar = strChar[startIndex];

            strChar[startIndex] = strChar[endIndex];

            strChar[endIndex] = tempChar;

            startIndex++;

            endIndex--;

        }

        return new String(strChar);

    }

    public static string ReverseAWordUsingStack(string str){

        Stack<string> stack = new Stack<string>();

        string tempStr = "";

        for(var i=0; i < str.Length; i++)

        {

            if(str[i]==' ')

            {

                stack.Push(tempStr);

                tempStr="";

            }else{

                tempStr += str[i].ToString();   

            }

        }

        stack.Push(tempStr);

        string reverseString = "";

        while(stack.Count > 0){

            reverseString += stack.Pop();

            if(stack.Count > 0) reverseString += " ";

        }

        return reverseString;

    }

}