Trim a char array

Question

Background: I was invited to an interview at a high profile company and I was asked the following question before being told I failed the interview for the position (C#,mvc3,razor). I'm genuinely interested in how to solve this.

Question: "Write a method that takes a char array, trims whitespace, and returns the same array." After some thinking I was told to replace the whitespace with "\o".

I started with:

public static char[] Trim(char[] c)
    {
        for (int i = 0; i < c.Length; i++)
        {
            if (c[i] == '\r' || c[i] == '\n' || c[i] == '\t')
            {
                c[i] = '\o';
            }     
        }
    }

I was told I have to use the same array, can't put it in a list and call ToArray(). However I think if the array stays the same size it is impossible to "trim it".

Answer 1

They may have meant \0 (NUL character), not dash-0

Answer 2

Assuming they meant to replace whitespace characters with null characters then the solution is simple:

Step 1: From the start of the string (represented as a character array) replace whitespace characters until a non-WS character is encountered.

Step 2: From the end of the string, working backwards, do the same.

public static void Trim( Char[] chars )
{        
    int maxIdx = 0; // an optimization so it doesn't iterate through chars already encountered
    for( int i = 0;i < chars.Length; i++ )
    {
        if( Char.IsWhitespace( chars[i] ) )
        {
            chars[i] = '\0';
        }
        else
        {
            maxIdx = i;
            break;
        }
    }

    for( int i = chars.Length - 1; i > maxIdx; i-- )
    {
        if( Char.IsWhitespace( chars[i] ) ) chars[i] = '\0';
    }
}

Answer 3

public static char[] Trim(char[] str)
{
  return str.Where(x => !Char.IsWhiteSpace(x)).ToArray();
}