TweetFollow Us on Twitter

Apr 00 Challenge

Volume Number: 16 (2000)
Issue Number: 4
Column Tag: Programmer's Challenge

Programmer's Challenge

by Bob Boonstra, Westford, MA

Text Compression

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.

Three Months Ago Winner

Congratulations to Sebastian Maurer for winning the January, 2000, Triangle Peg Challenge. The Peg Challenge required entries to solve variously sized games of peg solitaire, a game where pegs are arranged in holes on a triangle board. The objective of the game is to repeatedly jump one peg over an adjacent one, removing the jumped peg each time, with the intent of removing as many pegs as possible. In our Challenge, scoring counted 1000 penalty points for each peg left on the board, plus one penalty point for each millisecond of execution time. Sebastian did not submit the fastest entry - in fact, he ranked third in speed - but it played the Peg game significantly better than the other solutions, resulting in a better overall score.

I evaluated the Pegs entries using 14 test cases, ranging from 5 pegs to 100 pegs on a side. Nine of the test cases were missing only one peg, one of the large puzzles was missing 50 pegs, with the remainder missing a small number of pegs. Sebastian's entry left fewer pegs on the board than the second place solution in 12 of 14 test cases, and fewer than the third place solution in 10 of 14 cases. Sebastian's entry won in all of the test cases involving larger puzzles.

Sebastian's code is rather sparsely commented. The work is done in his Search routine, which iteratively tries valid moves, backtracks when it cannot find a valid move, and saves the best solution found so far. In looking at the code for the top entries, it wasn't obvious why Sebastian's solution did so much better than the others. The entries did use different logic to prune the search and trade execution time against search depth; perhaps those differences explain the performance variation.

The table below lists, for each of the solutions submitted, the overall score, the execution time in microseconds, and the total number of pegs left on the board for all of our test cases. It also indicates the code size, data size, and programming language used by each solution. Two entries did not complete all of the test cases and are listed last. As usual, the number in parentheses after the entrant's name is the total number of Challenge points earned in all Challenges prior to this one.

NameScoreTime (µsecs)Pegs LeftCode SizeData SizeLang
Sebastian Maurer (77)20224644646419764852162C
Andrew Downs (2)3623988109883613187220C
Willeke Rieken (61)3727672146723713302056C++
Randy Boring (112)11211715476714107357308132096C++
M. L.N/AN/A2648218C
J. C.N/AN/A108281021C++

Top Contestants

Listed here are the Top Contestants for the Programmer's Challenge, including everyone who has accumulated 10 or more points during the past two years. The numbers below include points awarded over the 24 most recent contests, including points earned by this month's entrants.

1.Munter, Ernst227
2.Saxton, Tom139
3.Maurer, Sebastian87
4.Rieken, Willeke48
5.Boring, Randy43
6.Heithcock, JG43
7.Shearer, Rob43
8.Taylor, Jonathan24
9.Brown, Pat20
10.Downs, Andrew12
11.Jones, Dennis12
12.Hart, Alan11
13.Duga, Brady10
14.Hewett, Kevin10
15.Murphy, ACC10
16.Selengut, Jared10
17.Strout, Joe10
18.Varilly, Patrick10

There are three ways to earn points: (1) scoring in the top 5 of any Challenge, (2) being the first person to find a bug in a published winning solution or, (3) being the first person to suggest a Challenge that I use. The points you can win are:

1st place20 points
2nd place10 points
3rd place7 points
4th place4 points
5th place2 points
finding bug2 points
suggesting Challenge2 points

Here is Sebastian's winning Triangle Peg solution:

Copyright © 2000 Sebastian Maurer

#include "Pegs.h"
#include "Memory.h"
#include "Timer.h"

#include <stdio.h>

const int kNumTries = 1000;
const UInt32 kStopTime = 500000;
  // in microseconds

const int kNumDirections = 6;
enum {kIllegal = 0, kFull, kEmpty};

char** gGrid;
PegJump *gCurrentJumps;
PegJump *gBestJumps;
int gBestScore;
UnsignedWide gLastImprovement;
unsigned short *gDirection;
short gDeltaRow[kNumDirections];
short gDeltaCol[kNumDirections];

static UInt32 WideDiff(UnsignedWide m1, UnsignedWide m2)
  UnsignedWide m;
  m.lo = m2.lo - m1.lo;
  m.hi = m2.hi - m1.hi;
  if (m1.lo > m2.lo)
    m.hi -= 1;
  return m.lo;

static void PrintBoard(int triangleSize) {
  for(int r = 0; r < triangleSize; r++) {
    for(int c = - triangleSize; c <= triangleSize; c++)
      switch (gGrid[r][c]) {
        case kIllegal: printf(" "); break;
        case kFull: printf("X"); break;
        case kEmpty: printf("."); break;
        default: printf("?");

// Memory allocation for the 2D grid
static char **AllocateGrid(
  int xMin, int xMax,
  int yMin, int yMax)
  int i, j;
  int nx = xMax - xMin + 1;
  int ny = yMax - yMin + 1;
  char **array;
  Ptr p;
  int rowSize;

  array = (char **) NewPtr((Size)(nx * sizeof(char*)));
  if (array == 0)
    return 0;
  array -= xMin;
  p = NewPtr((Size)(nx * ny * sizeof(char)));
  if (p == 0)
    return 0;
  p -= yMin * sizeof(char);
  rowSize = (int)(ny * sizeof(char));
  for(i = xMin; i <= xMax; i++) {
    array[i] = (char*) p;
    p += rowSize;

  for(i = xMin; i <= xMax; i++)
    for(j = yMin; j <= yMax; j++)
      array[i][j] = 0;

  return array;

static void DeallocateGrid(
  char **array, long xMin, long yMin)
  DisposePtr((Ptr) (array[xMin] + yMin));
  DisposePtr((Ptr) (array + xMin));

// Fill the grid with the initial configuration
static void FillGrid(
  short size,
  short numInitialPegs,
  TrianglePegPosition initialPegPositions[]
) {
  for(int r = -2; r < size + 2; r++)
    for(int c = - size - 2; c <= size + 2; c++)
      gGrid[r][c] = kIllegal;

  for(int r = 0; r < size; r++)
    for(int c = - r; c <= r; c += 2)
      gGrid[r][c] = kEmpty;
  for(int p = 0; p < numInitialPegs; p++) {
    int row = initialPegPositions[p].row;
    int col = initialPegPositions[p].col;
    gGrid[row][col] = kFull;

// Store the current best solution
static void SaveSolution(int numMoves) {
  gBestScore = numMoves;

  for(int m = 0; m < numMoves; m++) {
    gBestJumps[m].from.row =
    gBestJumps[m].from.col =
    gBestJumps[m].to.row =
    gBestJumps[m].to.col =

// Perform a move if it is legal, and return true
// If the move is illegal, return false
// I assume position (r,c) already contains a peg
static bool Try(int move, int r, int c, int dir)
  int dr = gDeltaRow[dir];
  int dc = gDeltaCol[dir];

  if ((gGrid[r + dr][c + dc] == kFull) &&
    (gGrid[r + 2 * dr][c + 2 * dc] == kEmpty))
    gDirection[move] = dir;
    gCurrentJumps[move].from.row = r;
    gCurrentJumps[move].from.col = c;
    gCurrentJumps[move].to.row = r + 2 * dr;
    gCurrentJumps[move].to.col = c + 2 * dc;
    gGrid[r][c] = kEmpty;
    gGrid[r + dr][c + dc] = kEmpty;
    gGrid[r + 2 * dr][c + 2 * dc] = kFull;

    return true;
    return false;

// Undo a move by restoring the grid
static inline void UndoMove(int row, int col, int dir) {
  int dr = gDeltaRow[dir];
  int dc = gDeltaCol[dir];

  gGrid[row][col] = kFull;
  gGrid[row + dr][col + dc] = kFull;
  gGrid[row + 2 * dr][col + 2 * dc] = kEmpty;

// This is where the search is done
static void Search(
  int numInitialPegs,
  int triangleSize
) {

  UnsignedWide now;
  int move, row, col, dir;
  bool abort = false;
  bool haveASolution = false;
  int numTries = 0;

  row = 0;
  col = 0;
  dir = -1;
  move = 0;

  do {
    // find the next valid move
    do {
      if (dir >= kNumDirections) {
        dir = 0;
        if (col == row + 1) {
          col = - row;
    } while ((row < triangleSize) &&
           ((gGrid[row][col] == kEmpty) ||
            !Try(move, row, col, dir)));
    if (row < triangleSize) {
      // we just made a valid move
      // start work on the next move

      row = 0;
      col = 0;
      dir = 0;
    } else { // we reached a dead end
      // see if this is a better solution
      if (move > gBestScore) {
        haveASolution = true;

        if (move + 1 == numInitialPegs)
          abort = true;


        gLastImprovement = now;
      // backtrack
      if (move >= 0) {
        row = gCurrentJumps[move].from.row;
        col = gCurrentJumps[move].from.col;
        dir = gDirection[move];
        UndoMove(row, col, dir);        
    if (haveASolution) {
      // if we already reached a dead end once,
      // don't waste time searching more
      if (numTries == kNumTries) {
        numTries = 0;
        if (WideDiff(gLastImprovement, now) >
          abort = true;

  } while (!abort && (move >= 0));

short /* number of moves */ SolvePegTriangle (
  short triangleSize,
    /* number of rows in triangle to solve */
  short numInitialPegs,
    /* number of pegs in starting puzzle position */
  TrianglePegPosition initialPegPositions[],
    /* peg locations in starting puzzle position */
  PegJump pegJumps[]
    /* return peg moves that solve the puzzle here,
       in sequence */

) {
  // prepare, allocate, initialize structures
  gDeltaRow[0] = -1; gDeltaCol[0] = -1;
  gDeltaRow[1] = -1; gDeltaCol[1] = +1;
  gDeltaRow[2] = 0; gDeltaCol[2] = -2;
  gDeltaRow[3] = 0; gDeltaCol[3] = +2;
  gDeltaRow[4] = +1; gDeltaCol[4] = -1;
  gDeltaRow[5] = +1; gDeltaCol[5] = +1;
  gGrid =
    AllocateGrid(-2, triangleSize + 2,
      - triangleSize - 2, triangleSize + 2);
  if (gGrid == 0)
    return 0;
  gDirection = (unsigned short*)
    NewPtr(numInitialPegs * sizeof(unsigned short));
  if (gDirection == 0)
    return 0;
  gCurrentJumps = (PegJump*)
    NewPtr(numInitialPegs * sizeof(PegJump));
  if (gCurrentJumps == 0)
    return 0;

  gBestJumps = pegJumps;

  gBestScore = 0;

  FillGrid(triangleSize, numInitialPegs,

  // do the work
  Search(numInitialPegs, triangleSize);

  // clean up
  DeallocateGrid(gGrid, -2, - triangleSize - 2);

  return gBestScore;

Community Search:
MacTech Search:

Software Updates via MacUpdate

Sago Mini Superhero (Education)
Sago Mini Superhero 1.0 Device: iOS Universal Category: Education Price: $2.99, Version: 1.0 (iTunes) Description: KAPOW! Jack the rabbit bursts into the sky as the Sago Mini Superhero! Fly with Jack as he lifts impossible weights,... | Read more »
Star Wars: Galaxy of Heroes guide - How...
Star Wars: Galaxy of Heroes is all about collecting heroes, powering them up, and using them together to defeat your foes. It's pretty straightforward stuff for the most part, but increasing your characters' stats can be a bit confusing because it... | Read more »
The best cooking apps (just in time for...
It’s that time of year again, where you’ll be gathering around the dinner table with your family and a huge feast in front of you. [Read more] | Read more »
Square Rave guide - How to grab those te...
Square Rave is an awesome little music-oriented puzzle game that smacks of games like Lumines, but with its own unique sense of gameplay. To help wrap your head around the game, keep the following tips and tricks in mind. [Read more] | Read more »
Snowboard Party 2 (Games)
Snowboard Party 2 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Crowned the best snowboarding game available on the market, Snowboard Party is back to fulfill all your adrenaline needs in... | Read more »
One Button Travel (Games)
One Button Travel 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: “To cut a long story short, If you like interactive fiction, just go buy this one.” - “Oozes the polish that... | Read more »
Light Apprentice Volume 1 (Games)
Light Apprentice Volume 1 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Light Apprentice Volume 1 includes Chapters 1 to 4, all gathered in a new exclusive game. When life in the world of... | Read more »
The best games like Animal Crossing on m...
Animal Crossing amiibo Festival is out right now for the Wii U, reminding us of just how much fun that world can be. Or at least to go back and check in on our villages once in a while. [Read more] | Read more »
Between 2 Taps - Tap for Tap interview M...
Hello, and welcome back to Between 2 Taps, Tap for Tap’s Indie Dev interview series. [Read more] | Read more »
Facility 47 (Games)
Facility 47 1.0.1 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0.1 (iTunes) Description: You wake up alone and freezing in an icy cell. You try the cell door but it’s locked, it seems that you are stuck with no... | Read more »

Price Scanner via

Black Friday deals on the Apple Watch and App...
Apple resellers are offering discounts and bundles with the purchase of an Apple Watch this Black Friday weekend. Below is a roundup of the deals being offered by authorized Watch resellers: Apple... Read more
Early Black Friday sale at B&H Photo, up...
B&H Photo has all new Macs on sale for up to $500 off MSRP as part of their early Black Friday sale including free shipping plus NY sales tax only: - 15″ 2.2GHz Retina MacBook Pro: $1699 $300 off... Read more
NewerTech/OWC/MacSales Black Friday Deals 201... • Free Shipping available on nearly EVERYTHING on orders $35.00 & up within USA + • International Delivery Specials from $2.99+ Special Purolator... Read more
Walmart Black Friday deals: $100 off select i...
Walmart has released their Black Friday deals for 2015, now available online. Choose free shipping or free local store pickup (if available): - 16GB iPad Air 2: $399, $100 off MSRP - 16GB iPad Air: $... Read more
Photo Cleaner 1.0 Reclaims iPhone Storage Spa...
Seoul, Korea based mix1009 has announced the release and immediate availability of Photo Cleaner 1.0, their handy iPhone app that deletes the video portion of Live Photos, in order to reclaim space... Read more
Black Friday and Holiday sales on our price t...
Scan our Mac Price Trackers for the latest Black Friday and Holiday season information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the... Read more
Best Buy Black Friday deals: Up to $200 off M...
Best Buy has posted their Black Friday sale prices for 2015. Save on MacBook Pros, MacBooks, MacBook Airs, iMacs, iPads, and Apple Watches. Choose free shipping or free local store pickup (if... Read more
Save $30-$40 on new Apple TVs after rebate
Adorama has new Apple TVs on sale for up to $40 off MSRP after mail-in rebate, good through December 15th. Shipping is free, and Adorama charges NY & NJ sales tax only: - 32GB Apple TV: $119.99... Read more
13-Inch Haswell MacBook Air At Two Years – Th...
The 13-inch mid-2013 “Haswell” MacBook Air I ordered in Apple’s November 2013 Black Friday sale was my first new Mac in four and a half years — the longest interval I’ve gone between system upgrades... Read more
Target Black Friday Early Access deals: $100...
Target is offering early access to their Black Friday deals on Apple products on their online store for today, the 25th, only. Choose free shipping or free local store pickup (if available): - Apple... Read more

Jobs Board

*Apple* Enterprise / Government Professional...
# Apple Enterprise / Gove ment Professional Services Engineer Job Number: 42292976 Reston, Virginia, United States Posted: Aug. 18, 2015 Weekly Hours: 40.00 **Job Read more
iOS Wallet & *Apple* Pay Engineer - App...
# iOS Wallet & Apple Pay Engineer Job Number: 40586801 Santa Clara Valley, Califo ia, United States Posted: Nov. 16, 2015 Weekly Hours: 40.00 **Job Summary** The iOS Read more
Software Engineer, *Apple* Watch - Clock Fa...
# Software Engineer, Apple Watch - Clock Face Team Job Number: 44368761 Santa Clara Valley, Califo ia, United States Posted: Nov. 14, 2015 Weekly Hours: 40.00 **Job Read more
Administrative Assistant, *Apple* Online St...
# Administrative Assistant, Apple Online Store Job Number: 43992352 Santa Clara Valley, Califo ia, United States Posted: Nov. 9, 2015 Weekly Hours: 40.00 **Job Summary** Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.