Appending Strings in Java/C# without using StringBuffer.Append or StringBuilder.Append

Question

at a recent interview I attended, the programming question that was asked was this. Write a function that will take as input two strings. The output should be the result of concatenation.

Conditions: Should not use StringBuffer.Append or StringBuilder.Append or string objects for concatenation;that is, they want me to implement the pseudo code implementation of How StringBuilder or StringBuffer's Append function works.

This is what I did:

    static char[] AppendStrings(string input, string append)
    {
        char[] inputCharArray = input.ToCharArray();
        char[] appendCharArray = append.ToCharArray();
        char[] outputCharArray = new char[inputCharArray.Length + appendCharArray.Length];
        for (int i = 0; i < inputCharArray.Length; i++)
        {
            outputCharArray[i] = inputCharArray[i];
        }
        for (int i = 0; i < appendCharArray.Length; i++)
        {
            outputCharArray[input.Length + i] = appendCharArray[i];
        }
        return outputCharArray;
    }

While this is a working solution, is there a better way of doing things?

Answer 1

is LINQ legal? strings are just can be treated as an enumeration of chars, so they can be used with LINQ (even though there is some cost involved, see comments):

string a = "foo";
string b = "bar";

string c = new string(a.AsEnumerable().Concat(b).ToArray());

or with your method signature:

 static char[] AppendStrings(string input, string append)
 {
   return input.AsEnumerable().Concat(append).ToArray();
 }