StringCoder free response answer 2008

StringCoder is #2 from the from the 2008 AP Computer Science A Free Response problems.

https://secure-media.collegeboard.org/apc/ap08_comp_sci_a_frq.pdf

Part (a) decodeString method

public String decodeString(ArrayList<StringPart> parts)
{
    String decoded = "";
    
    for(StringPart sp : parts)
        decoded += masterString.substring(
                sp.getStart(), sp.getStart() + sp.getLength());
    
    return decoded;
}

See more about manipulating Strings on the AP CS A Exam.

Part (b) encodeString method

public ArrayList<StringPart> encodeString(String word)
{
    ArrayList<StringPart> parts = new ArrayList<StringPart>();
    
    String wordRemaining = word;
    
    while(wordRemaining.length() > 0)
    {
        StringPart sp = findPart(wordRemaining);
        parts.add(sp);
        wordRemaining = wordRemaining.substring(sp.getLength());
    }
    
    return parts;
}

findPart method (not required on Exam)

StringPart findPart(String str)
{
    String strPart = str;
    
    int index = masterString.indexOf(strPart);
    
    while(index == -1)
    {
        strPart = strPart.substring(0, strPart.length() - 1);
        index = masterString.indexOf(strPart);
    }
    
    return new StringPart(index, strPart.length());
}

This implementation finds the largest part of the beginning of str that exists in masterString.

2008 AP CS Exam Free Response Solutions

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