Interview question

string.Replace("\r\n\r\n", "\r\n \r\n");

Good one Robert, I like it, its simpler than mine.

string insertSpaceBetweenLineBreaks(string input)

{

   return Regex.Replace(input, "(\r\n)(\\1)", "$1 $2");

}

Beaten to it. I was thinking exactly the same as Robert.

I'm afraid it's not that easy. What about \r\n\r\n\r\n ? :)

As Ben mentionned, you need to take care of more than 2 consecutive breaks. I think it is necessary to iterate through the chars and create a new string as you go (which isn't an optimum solution):

string text = "hello \r\n\r\n\r\n world!";

string textResult = "";

char[] caFromText = text.ToCharArray();

for (int i = 0; i < caFromText.Length; ++i)

{

textResult += caFromText[i];

if ((int)caFromText[i] == CARRIAGE_RETURN)

{

 // check if not reaching the end of the array

 if (i + 3 < caFromText.Length)

 {

  if ((int)caFromText[i + 1] == NEW_LINE

  && (int)caFromText[i + 2] == CARRIAGE_RETURN

  && (int)caFromText[i + 3] == NEW_LINE)

  {

   // two consecutive breaks where detected

   textResult += "\n ";

   // jump to the next break

   ++i;

  }

 }

}

}

Hmmm, this version works via loop but I'd like to see a recursive version.

This version uses a dash instead of space so its easy to see result.

string insertSpaceBetweenLineBreaks(string input)

{

   while (Regex.Match(input, "(\r\n)(\\1)").Success)

   {

       input = Regex.Replace(input, "(\r\n)(\\1)", "$1-$1");

   }

   return input;

}

The test string I used was "A\r\nB\r\n\r\nC\r\n\r\n\r\nD\r\n\r\n\r\n\r\nE".

This is the result

A

B

-

C

-

-

D

-

-

-

E

Recursive version, same result as previous while loop version.

string insertSpaceBetweenLineBreaksRec(string input)

{

   if (!Regex.Match(input, "(\r\n)(\\1)").Success)

   {

       return input;

   }

   else

   {

       input = Regex.Replace(input, "(\r\n)(\\1)", "$1-$1");

       return insertSpaceBetweenLineBreaksRec(input);

   }

}

In terms of why you might want this - SMTP?

Slightly faster :

public static string Method3(string input)

       {

           int startIndex = 0;

           var sb = new StringBuilder(input.Length * 2);

           while (true)

           {

               int index = input.IndexOf("\r\n", startIndex);

               if (index == -1)

               {

                   break;

               }

               int length = index - startIndex;

               sb.Append(input.Substring(startIndex, length));

               if (length == 1)

               {

                   sb.Append("-");

               }

               startIndex = index + 1;

           }

           return sb.ToString();

       }

Not much of a difference though.

straigtforward solution

let insertSpaces (s : string) =

   let rec loop (i : int) acc =

       let newIndex = s.IndexOf("\r\n\r\n", i)

       if newIndex = -1 then acc + s.Substring(i)

       else loop (newIndex + 2) (acc + s.Substring(i, newIndex - i) + "\r\n ")

   loop 0 ""

or

let insertSpaces2 (s : string) =

   let checkCrlf i =

       if i < s.Length - 1 then s.[i] = '\r' && s.[i+1] = '\n'

       else false

   let rec loop i crlf (acc : System.Text.StringBuilder) =

       if i >= s.Length then acc.ToString()

       else

           let found = checkCrlf i

           match found, crlf with

           | true, true -> loop i false (acc.Append(' '))

           | true, false -> loop (i + 2) true (acc.Append("\r\n"))

           | false, _ -> loop (i + 1) false (acc.Append(s.[i]))

   loop 0 false (new System.Text.StringBuilder())

Here's my take at it :

       public static string InsertSpacesBetweenLineBreaks(string s)

       {

           StringBuilder sb = new StringBuilder();

           bool prevCrLf = false;

           char prev = '\0';

           foreach (char c in s)

           {

               if (c == '\n' && prev == '\r')

               {

                   if (prevCrLf) sb.Append(' ');

                   prevCrLf = true;

               }

               else if (c != '\r')

               {

                   prevCrLf = false;

               }

               sb.Append(c);

               prev = c;

           }

           return sb.ToString();

       }