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April 2000 Programmer's Challenge
Text Compression
Mail solutions to:
progchallenge@mactech.com
Due Date: 11:59pm ET, Saturday, 1 April 2000
This month, we’ve got some very important messages to send. But we’re not living in a world of free bandwidth. In fact, bandwidth in our Challenge world is very expensive, so expensive that we’re asking you to compress our messages and save us a few bytes.
The prototype for the code you should write is:
void * /* yourStorage */ InitCompression(void);
long /* compressedLength */ CompressText(
char *inputText, /* text to be compressed */
long numInputChars, /* length of inputText in bytes */
char *compressedText, /* return compressedText here */
const void *yourStorage /* storage returned by InitCompression */
);
long /* expandedLength */ ExpandText(
char *compressedText, /* encoded text to be expanded */
long compressedLength, /* length of encoded text in bytes */
char *expandedText, /* return expanded text here */
const void *yourStorage /* storage returned by InitCompression */
);
void TermCompression(
void *yourStorage /* storage returned by InitCompression */
);
For this Challenge, you need to provide the four routines indicated above. Your InitCompression and TermCompression routines will be called only once each, at the beginning of the test and at the end of the test, respectively. InitCompression should allocate and return a block of yourStorage where you initialize any information needed by your compression and expansion routines. That storage will be passed back to you unchanged each time you are asked to compress or decompress text. TermCompression will be called at the end of the test and should deallocate the block of yourStorage to avoid a memory leak.
In between the calls to InitCompression and TermCompression, the test code will make multiple calls to CompressText and ExpandText with different inputText values. CompressText should process the inputText, populate the compressedText, and return the number of bytes in the result. ExpandText does the opposite, processing the compressedText, converting it to expandedText, and returning the number of bytes of the original text. Multiple CompressText and ExpandText calls will occur with varying inputText and compressedText, in any order, with the obvious constraint that text must be encoded before it can be decoded.
The inputText may contain any character between 0x00 and 0x7F, inclusive. As a practical matter, the inputText will be drawn from paragraphs of English-language text, computer programs in C, C++, and Pascal, and html pages.
All text-specific information needed to decode the compressedText must be stored in the compressedText itself. Any text-independent decoding information may be stored in yourStorage or in static storage within your program. No text-specific encoding information may be stored in yourStorage or in static variables.
The winner will be the solution that correctly compresses the inputText into the least costly compressedText, where cost is a function of length and execution time. Specifically, each inputText will have a cost equal to theCompressedLength of the corresponding compressedText, plus a penalty of 10% for each 100 milliseconds required to do the encoding and decoding.
This will be a native PowerPC Challenge, using the CodeWarrior Pro 5 environment. Solutions may be coded in C, C++, or Pascal. Solutions in Java will also be accepted, but Java entries must be accompanied by a test driver that uses the interface provided in the problem statement.
Test code for this Challenge is available.
You can get a head start on the Challenge by reading the
Programmer's Challenge mailing list. It will be posted to the list on
or before the 12th of the preceding month. To join, send an email to
listserv@listmail.xplain.com
with the subject "subscribe challenge-A". You can also join the
discussion list by sending a message with the subject "subscribe
challenge-D".
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