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.

RankNamePoints
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:

Pegs.c
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("?");
      }
    }
    printf("\n");
  }
  printf("\n");
}

AllocateGrid
//////
// 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;
}

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

FillGrid
//////
// 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;
  }
}

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

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

Try
//////
// 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;
  }
  else
    return false;
}

UndoMove
//////
// 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;
}

Search
//////
// 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 {
      dir++;
      if (dir >= kNumDirections) {
        dir = 0;
        col++;
        if (col == row + 1) {
          row++;
          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
      
      move++;

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

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

        Microseconds(&now);

        gLastImprovement = now;
      }
      
      // backtrack
      move-;
      
      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
    
      numTries++;
      if (numTries == kNumTries) {
        numTries = 0;
        Microseconds(&now);
        if (WideDiff(gLastImprovement, now) >
            kStopTime)
        {
          abort = true;
        }
      }
    }

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

SolvePegTriangle
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;

  Microseconds(&gLastImprovement);
  gBestScore = 0;

  FillGrid(triangleSize, numInitialPegs,
       initialPegPositions);

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

  // clean up
  DeallocateGrid(gGrid, -2, - triangleSize - 2);
  DisposePtr((Ptr)gDirection);
  DisposePtr((Ptr)gCurrentJumps);

  return gBestScore;
}
 
AAPL
$100.96
Apple Inc.
-0.83
MSFT
$47.52
Microsoft Corpora
+0.84
GOOG
$596.08
Google Inc.
+6.81

MacTech Search:
Community Search:

Software Updates via MacUpdate

Audio Hijack Pro 2.11.3 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more
Airfoil 4.8.9 - Send audio from any app...
Airfoil allows you to send any audio to AirPort Express units, Apple TVs, and even other Macs and PCs, all in sync! It's your audio - everywhere. With Airfoil you can take audio from any... Read more
WhatRoute 1.13.0 - Geographically trace...
WhatRoute is designed to find the names of all the routers an IP packet passes through on its way from your Mac to a destination host. It also measures the round-trip time from your Mac to the... Read more
Chromium 37.0.2062.122 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. FreeSMUG-Free OpenSource Mac User Group build is... Read more
Attachment Tamer 3.1.14b9 - Take control...
Attachment Tamer gives you control over attachment handling in Apple Mail. It fixes the most annoying Apple Mail flaws, ensures compatibility with other email software, and allows you to set up how... Read more
Duplicate Annihilator 5.0 - Find and del...
Duplicate Annihilator takes on the time-consuming task of comparing the images in your iPhoto library using effective algorithms to make sure that no duplicate escapes. Duplicate Annihilator detects... Read more
jAlbum Pro 12.2 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code!... Read more
jAlbum 12.2 - Create custom photo galler...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results Simply drag and drop photos into groups, choose a design... Read more
Quicken 2015 2.0.4 - Complete personal f...
Quicken 2015 helps you manage all your personal finances in one place, so you can see where you're spending and where you can save. Quicken automatically categorizes your financial transactions,... Read more
iMazing 1.0 - Complete iOS device manage...
iMazing (formerly DiskAid) is the ultimate iOS device manager with capabilities far beyond what iTunes offers. With iMazing and your iOS device (iPhone, iPad, or iPod), you can: Copy music to and... Read more

Latest Forum Discussions

See All

View Source – HTML, JavaScript and CSS...
View Source – HTML, JavaScript and CSS 1.0 Device: iOS Universal Category: Utilities Price: $.99, Version: 1.0 (iTunes) Description: View Source is an app plus an iOS 8 Safari extension that makes it easy to do one key web developer... | Read more »
Avenged Sevenfold’s Hail To The King: De...
Avenged Sevenfold’s Hail To The King: Deathbat is Coming to iOS on October 16th Posted by Jessica Fisher on September 19th, 2014 [ permalink ] Just in time for Halloween, on October 16 Avenged Sevenfold will be launching | Read more »
Talisman Has Gone Universal – Can Now be...
Talisman Has Gone Universal – Can Now be Played on the iPhone Posted by Jessica Fisher on September 19th, 2014 [ permalink ] | Read more »
Tap Army Review
Tap Army Review By Jennifer Allen on September 19th, 2014 Our Rating: :: SHOOT EM ALLUniversal App - Designed for iPhone and iPad Mindless but fun, Tap Army is a lane-based shooter that should help you relieve some stress.   | Read more »
Monsters! Volcanoes! Loot! Epic Island f...
Monsters! Volcanoes! Loot! | Read more »
Plunder Pirates: Tips, Tricks, Strategie...
Ahoy There, Seadogs: Interested in knowing our thoughts on all this plundering and pirating? Check out our Plunder Pirates Review! Have you just downloaded the rather enjoyable pirate-em-up Plunder Pirates and are in need of some assistance? Never... | Read more »
Goat Simulator Review
Goat Simulator Review By Lee Hamlet on September 19th, 2014 Our Rating: :: THE GRUFFEST OF BILLY GOATSUniversal App - Designed for iPhone and iPad Unleash chaos as a grumpy goat in this humorous but short-lived casual game.   | Read more »
A New and Improved Wunderlist is Here fo...
A New and Improved Wunderlist is Here for iOS 8 Posted by Jessica Fisher on September 19th, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Evernote Update for iOS 8 Adds Web Clipp...
Evernote Update for iOS 8 Adds Web Clipping, Quick Notes, and More Posted by Ellis Spice on September 19th, 2014 [ permalink ] | Read more »
Apple Names Ultimate Productivity Bundl...
Apple Names Ultimate Productivity Bundle by Readdle as the Essential Bundle on the App Store Posted by Jessica Fisher on September 19th, 2014 [ permalink | Read more »

Price Scanner via MacPrices.net

iFixIt Tears Down iPhone 6; Awards Respectabl...
iFixit notes that even the smaller 4.7″ iPhone 6 is a giant among iPhones; so big that Apple couldn’t fit it into the familiar iPhone form factor. In a welcome reversal of a recent trend to more or... Read more
Phone 6 Guide – Tips Book For Both iPhone 6...
iOS Guides has announced its latest eBook: iPhone 6 Guide. Brought to you by the expert team at iOS Guides, and written by best-selling technology author Tom Rudderham, iPhone 6 Guide is packed with... Read more
How to Upgrade iPhone iPad to iOS 8 without D...
PhoneClean, a iPhone cleaner utility offered by iMobie Inc., reveals a solution for upgrading iPhone and iPad to iOS 8 without deleting photos, apps, the new U2 album or anything. Thanks to more than... Read more
Inpaint 6 – Photo Retouching Tool Gets Faster...
TeoreX has announced Inpaint 6, a simple retouching tool for end users that helps remove scratches, watermarks, and timestamps as well as more complex objects like strangers, unwanted elements and... Read more
Worldwide PC Monitor Market Sees Growth in To...
Worldwide PC monitor shipments totaled 32.5 million units in the second quarter of 2014 (2Q14), a year-over-year decline of -2.9%, according to the International Data Corporation (IDC) Worldwide... Read more
Updated Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
Mac Pros available for up to $260 off MSRP
Adorama has Mac Pros on sale for up to $260 off MSRP. Shipping is free, and Adorama charges sales tax in NY & NJ only: - 4-core Mac Pro: $2839.99, $160 off MSRP - 6-core Mac Pro: $3739.99, $260... Read more
13-inch 2.6GHz/256GB Retina MacBook Pros avai...
B&H Photo has the 13″ 2.6GHz/256GB Retina MacBook Pro on sale for $1379 including free shipping plus NY sales tax only. Their price is $120 off MSRP. Read more
Previous-generation 15-inch 2.0GHz Retina Mac...
B&H Photo has leftover previous-generation 15″ 2.0GHz Retina MacBook Pros now available for $1599 including free shipping plus NY sales tax only. Their price is $400 off original MSRP. B&H... Read more
21″ 2.7GHz iMac available for $1179, save $12...
Adorama has 21″ 2.7GHz Hawell iMacs on sale for $1179.99 including free shipping. Their price is $120 off MSRP. NY and NJ sales tax only. Read more

Jobs Board

*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
Position Opening at *Apple* - Apple (United...
**Job Summary** At the Apple Store, you connect business professionals and entrepreneurs with the tools they need in order to put Apple solutions to work in their Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** The Apple Store is a retail environment like no other - uniquely focused on delivering amazing customer experiences. As an Expert, you introduce people Read more
Position Opening at *Apple* - Apple (United...
**Job Summary** As businesses discover the power of Apple computers and mobile devices, it's your job - as a Solutions Engineer - to show them how to introduce these Read more
Position Opening at *Apple* - Apple (United...
…Summary** As a Specialist, you help create the energy and excitement around Apple products, providing the right solutions and getting products into customers' hands. You Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.