Custom String converter.

[Raghu Devatha]

Hi,

I was doing an exercise and wanted to know if my code is efficient.

Input="aaabbaccaab"
Expected Output=a3b2a1c2a2b1

public class StringConvertCustom {
    public static void main(String args[]) {
        String input = "aaabbaccaab";
        char store;
        char[] tempOut;
        int i = 0, counter = 1;

        StringBuffer result = new StringBuffer();
        tempOut = input.toCharArray();

        result.append(tempOut[i]);

        store = tempOut[i];
        for (i = 1; i < tempOut.length; i++) {
            if (store == tempOut[i]) {
                counter = counter + 1;
            } else {
                result.append(counter);
                result.append(tempOut[i]);
                counter = 1;
                store = tempOut[i];

            }
        }
        result.append(counter);
        System.out.println(result);
    }
}

I hope there is a better program.

[Jesper de Jong]

Your program looks OK. Are you unhappy with it, and is there a specific thing in the code that you are unhappy with? Can you explain what that is?

One small change would be to use StringBuilder instead of StringBuffer - StringBuilder is a newer version of StringBuffer that doesn't have unnecessary synchronization. You will not notice any speed difference from making that change though in such a small and simple program.

In line 16, you could write counter++; instead of counter = counter + 1; but that doesn't make the code any more efficient.

[Raghu Devatha]

Thanks Jesper.

When I showed it to my instructor his first impression was I was using too many variables (increasing memory footprint). I was trying to reduce the number of variables used without loosing the readability.

Thanks again for the information on StringBuilder.

[Rob Spoor]

Don't use toCharArray() and tempOut, use String's own length() and charAt(int) methods. That way, you don't need to copy the entire String's contents into a new char[]. Because that's what toCharArray() does.

Now, about the number of variables:
- input: you'll need it. That's the String to convert.
- store: you'll need it. How else can you determine when to start a new counter?
- tempOut: you can get rid of this because of my above statement.
- i: you'll need it. It's the loop counter.
- counter: you'll need it. How else can you determine how many times a character occurred?
- result: you'll need it.

So apart from tempOut you can't get rid of any of the variables.

[Raghu Devatha]

Thanks a lot Rob for you expert opinion. It really helps.

[Rob Spoor]

For your information, as a little exercise for myself I rewrote your code using a nested loop. Unless I do not cache c (my version of "store") I still have the same number of variables at 5.

public class Test
{
    public static void main(String[] args) throws Exception
    {
        String input = "aaabbaccaab";
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < input.length(); )
        {
            char c = input.charAt(i);
            result.append(c);
            int j = i + 1;
            while (j < input.length() && input.charAt(j) == c)
            {
                j++;
            }
            result.append(j - i);
            i = j;
        }
        System.out.println(result);
    }
}

In this code, "c" is the equivalent of "store" and your "counter" is equivalent to "j - i". My code only has one advantage over yours - it can handle empty Strings. For the rest there isn't much difference.