TweetFollow Us on Twitter

Feb 93 Challenge
Volume Number:9
Issue Number:2
Column Tag:Programmers' Challenge

Programmers' Challenge

By Mike Scanlin, MacTech Magazine Regular Contributing Author

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Surely one of the most interesting things about life is that it’s unpredictable. You’re never quite sure exactly what is going to happen next. Think about the possibilities: Without any warning whatsoever you could meet someone you haven’t seen for years, a meteor could slam into the side of your house, Elvis could reappear, or the MacTech Magazaine Programmers’ Challenge deadline could be moved up after it had been published. Just knowing that these types of things could happen certainly does keep one on one’s toes, no?

Surprise! Due to gremlins in the production room, the deadline for the Nov/Dec puzzle was stated as being Jan 1st instead of the correct date of Dec 1st. Our apologies. To be fair, we will honor all submissions received up until Jan 1st and if a better one than the winner given below comes in we will publish the new winner next month. Hopefully the gremlin traps we’ve set will prevent this from happening again. Or, since this is the second time this has happened, maybe this month’s Challenge should be to accurately guess its deadline date...

The if-nothing-better-comes-in-before-Jan-1st winner of the “Millions of Colors?” challenge is Tom Pinkerton (Wilmette, IL). While I applaud his use of a minimal initialization loop and hard-coded array indexes, there is one thing that could be improved. This loop:

 register long*  sInitPtr;
 register long i;

 sInitPtr = sBluListPtr;
 i = 64;
 while (i--) {
 sInitPtr[3] =
 sInitPtr[2] =
 sInitPtr[1] =
 sInitPtr[0] = -1;
 sInitPtr += 4;
 }

could be better written as:

 register long*  sInitPtr;
 register long i, minusOne;

 sInitPtr = sBluListPtr;
 minusOne = -1;
 i = 64*4;
 do {
 *sInitPtr++ = minusOne;
 } while (--i);

which executes faster and is fewer bytes. Other than that little nit, Tom’s solution is clever and well implemented.

New E-Mail Addresses!

In the quest for better ways to work the Programmers’ Challenge, we have added a series of e-mail addresses for the puzzle. Please use these addresses. AppleLink: MT.PROGCHAL, Internet: progchallenge@xplain.com, and CompuServe: 71552,174.

Remember, that you cannot send files over Internet, but you can just send a message with the code in the message.

Insane Anglo Warlord

Did anyone see Sneakers? The movie itself had extremely few redeeming qualities but there was an interesting effect that they did with the credits. The movie was about secret codes. Each person’s name that came up had the letters scrambled to make valid English words which would then descramble themselves to be the person’s name (without adding or deleting any letters). For instance, Robert Redford initially came up as Fort Red Border and then descrambled to Robert Redford through a series of letter rearrangement steps.

What I’d like to do is ask you to write the routine that would come up with Fort Red Border (or any other valid set of English words) when given Robert Redford as input. But that would require the use of a large word list that I’m almost positive Neil wouldn’t want to print in this tiny little column. So, instead, I’m going to ask for a subset of this effect. Given the starting string, the ending string and the desired number of steps, the challenge is to come up with the intermediate strings in an appropriately interesting way (which may or may not involve some randomness-your decision).

The prototype of the function you write is:

void Descramble(startString, endString, numSteps, 
 stepStringPtrs)
Str255  startString, endString;
unsigned short   numSteps;
Str255  *stepStringPtrs[20];

Example:

 Input:
 startString = “\pFORT RED BORDER”
 endString = “\pROBERT REDFORD ” <note space at end>
 numSteps = 4
 stepStringPtrs = <numSteps pointers to Str255s allocated
 by the caller>

 Output:
 *stepStringPtrs[0] = “\pROOR TED BFRDER”
 *stepStringPtrs[1] = “\pRORRET D BFODER”
 *stepStringPtrs[2] = “\pROBDET R RFORED”
 *stepStringPtrs[3] = “\pROBEDT RERFORD ”

You can assume the input and output strings each have the same number of uppercase letters, which is at least twice numSteps (i.e. the minimum string length for a 4 step puzzle is 8 characters). Each intermediate string should match the final string a little bit better than the previous one (in terms of the number of letters that are in their final correct positions). There is no “correct” algorithm here-it’s up to you to devise one (i.e. your solution does not need to exactly match the example output given here). Unlike previous Programmer Challenges, this one will be judged primarily on effect, not speed. I’m looking for a smooth transition from startString to endString (and if it’s really fast and small then that’s an extra bonus).

So, who can guess what you get if you rearrange the letters in “Ronald Wilson Reagan”?

Here is Tom’s winning solution to the Nov/Dec Challenge:

// UniqueRGBValues.c:
//   A function that returns the number of
//   unique colors found in a 24-bit RGB image.
// Author: Tom Pinkerton

unsigned long
UniqueRGBValues(Ptr baseAddress,
 short numRows, short numCols)
{
 Handle sBuffers = nil;
 long   sUniquePixels = 0;

// Allocate memory for the data
// structures. We will need:
// 256 x 4 bytes for the unique blue value table.
// 256 x 256 x 8 bytes for the Red/Green
//   intersection grid.
// numRows x numCols x 4 bytes for the
//   master blue list.
 sBuffers = NewHandle((((long)numRows *
  (long)numCols) * 4L) + 525312);
 if (sBuffers != nil) {
 
 // Setup pointers to the data structures.
 long*  sBluListPtr =
  (long*)((char*)*sBuffers + 0);
 long*  sRGTablePtr =
  (long*)((char*)*sBuffers + 1024);
 long*  sRGLinksPtr =
  (long*)((char*)*sBuffers + 525312);
 long*  sRGBase = nil;
 
// Initialize the Red/Green intersection
// grid and the master Blue list with 
// -1's.
 {
 register long*  sInitPtr;
 register long i;
 
// A -1 in this table means that the blue
// value for a particular Red/Green
// combination is not yet found.
 sInitPtr = sBluListPtr;
 i = 64;
 while (i--) {
 sInitPtr[3] =
 sInitPtr[2] =
 sInitPtr[1] =
 sInitPtr[0] = -1;
 sInitPtr += 4;
 }
 
// Only the blue list link need be
// initialized (first of two longs) for
// each element. A -1 means that a unique
// Red/Green pair represented by this
// intersection has not yet been found.
 sInitPtr = sRGTablePtr;
 i = 4096;
 while (i--) {
 sInitPtr[30] =
 sInitPtr[28] =
 sInitPtr[26] =
 sInitPtr[24] =
 sInitPtr[22] =
 sInitPtr[20] =
 sInitPtr[18] =
 sInitPtr[16] =
 sInitPtr[14] =
 sInitPtr[12] =
 sInitPtr[10] =
 sInitPtr[ 8] =
 sInitPtr[ 6] =
 sInitPtr[ 4] =
 sInitPtr[ 2] =
 sInitPtr[ 0] = -1;
 sInitPtr += 32;
 }
 }
 
// Scan the image to create a linked list of blue values at 
// each unique Red/Green intersection. Each element in the
// Red/Green intersection grid consists of the first link 
// of that intersection's blue list (initially -1) and a 
// link to the next Red/Green intersection which contains 
// a blue list. Whereas the Red/Green link is a pointer 
// to the next Red/Green intersection, a blue list link 
// holds an array index in its low order 3 bytes and an 
// actual blue value in its high order byte. The blue link
// index refers to an element in the master blue list. 
// Each master blue list element then points to the next 
// blue value link within a specific blue list or terminates 
// the list with a -1 value.
 {
 register unsigned char*
 sPixelsPtr = (unsigned char*)baseAddress;
 register long* sRGPtr;
 register long*  sLinkPtr = sRGLinksPtr;
 register long sLinkIndex = 0;
 register long sNumPixels = 
 (long)numRows * (long)numCols;
 
// For each pixel in the image, do the following.
 while (sNumPixels--) {
 
// Concatenate the red and green values to create an offset 
// used to point at the unique Red/Green element in the
// Red/Green intersection grid.
 sRGPtr = sRGTablePtr +
  ((((long)sPixelsPtr[1] << 8) |
  (long)sPixelsPtr[2]) << 1);
 
// If this is the first pixel with this particular Red/Green 
// combination, then add the Red/Green intersection to the
// Red/Green linked list.
 if (sRGPtr[0] == -1) {
 sRGPtr[1] = (long)sRGBase;
 sRGBase = sRGPtr;
 }
 
// Create a new blue link with the pixel's blue value and 
// add it to Red/Green intersection's blue list.
 *sLinkPtr = sRGPtr[0];
 sRGPtr[0] = sLinkIndex | ((long)sPixelsPtr[3] << 24);
 
// Increment stuff for the next go 'round.
 ++sLinkPtr;
 ++sLinkIndex;
 sPixelsPtr += 4;
 }
 }
 
// For each list of blue values at a unique Red/Green 
// intersection,  determine the number of unique blue
// values in that list. This calculates the number of unique 
// colors that have the same Red and Green values.
// Accumulating the number of unique colors at every 
// Red/Green intersection gives us the total 
// number of unique colors.
 {
 register long*  sRGPtr = sRGBase;
 register long*  sBlueBase = nil;
 register long*  sBluePtr;
 register long   sLinkIndex;
 
// For each Red/Green intersection found above, do the 
// following.
 while (sRGPtr != nil) {
 
// Walk the list of blue values for this Red/Green pair. 
// For each one, do the following.
 sLinkIndex = sRGPtr[0];
 while (sLinkIndex != -1) {
 
// Create a pointer to the unique blue value element.
 sBluePtr = sBluListPtr +
 ((unsigned long)sLinkIndex >> 24);
 
// A -1 here means that the unique R/G and B color has not 
// yet been counted.  Therefore, mark the fact that it has
// been counted by adding the element to a linked list 
// and incrementing the unique color count. The blue value 
// linked list is used later to quickly reset itself.
 if (*sBluePtr == -1) {
 *sBluePtr = (long)sBlueBase;
 sBlueBase = sBluePtr;
 ++sUniquePixels;
 }
 
// Get the next blue list link in the blue list.
 sLinkIndex = sRGLinksPtr[sLinkIndex & 0x00FFFFFF];
 }
 
// Reset the blue count list by walking its links and 
// replacing them again with -1's.
 sBluePtr = sBlueBase;
 while (sBluePtr != nil) {
 sBlueBase = (long*)*sBluePtr;
 *sBluePtr = -1;
 sBluePtr = sBlueBase;
 }
 sBlueBase = nil;
 
// Get next Red/Green intersection.
 sRGPtr = (long*)sRGPtr[1];
 }
 }
 
 DisposHandle(sBuffers);
 }
 return(sUniquePixels);
}

The Rules

Here’s how it works: Each month there will be a different programming challenge presented here. First, you must write some code that solves the challenge. Second, you must optimize your code (a lot). Then, submit your solution to MacTech Magazine (formerly MacTutor). A winner will be chosen based on code correctness, speed, size and elegance (in that order of importance) as well as the postmark of the answer. In the event of multiple equally desirable solutions, one winner will be chosen at random (with honorable mention, but no prize, given to the runners up). The prize for the best solution each month is $50 and a limited edition “The Winner! MacTech Magazine Programming Challenge” T-shirt (not to be found in stores).

In order to make fair comparisons between solutions, all solutions must be in ANSI compatible C. All entries will be tested with the FPU and 68020 flags turned off in THINK C. When timing routines, the latest version of THINK C will be used (with ANSI Settings plus “Honor ‘register’ first” and “Use Global Optimizer” turned on) so beware if you optimize for a different C compiler.

The solution and winners for this month’s Programmers’ Challenge will be published in the issue two months later. All submissions must be received by the 10th day of the month printed on the front of this issue.

All solutions should be marked “Attn: Programmers’ Challenge Solution” and sent to Xplain Corporation (the publishers of MacTech Magazine) via “snail mail” or preferably, e-mail - AppleLink: MT.PROGCHAL, Internet: progchallenge@xplain.com, and CompuServe: 71552,174. If you send via snail mail, please include a disk with the solution and all related files (including contact information). See page 2 for information on “How to Contact Xplain Corporation.”

MacTech Magazine reserves the right to publish any solution entered in the Programming Challenge of the Month and all entries are the property of MacTech Magazine upon submission. The submission falls under all the same conventions of an article submission.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Airmail 3.3.2 - Powerful, minimal email...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
Numi 3.15.1 - Menu-bar calculator suppor...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more
Airmail 3.3.2 - Powerful, minimal email...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
Numi 3.15.1 - Menu-bar calculator suppor...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more
TextSoap 8.4.1 - Automate tedious text d...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
TextSoap 8.4.1 - Automate tedious text d...
TextSoap can automatically remove unwanted characters, fix up messed up carriage returns, and do pretty much anything else that we can think of to text. Save time and effort. Be more productive. Stop... Read more
Backblaze 4.3.0.44 - Online backup servi...
Backblaze is an online backup service designed from the ground-up for the Mac. With unlimited storage available for $5 per month, as well as a free 15-day trial, peace of mind is within reach with... Read more
Numi 3.15 - Menu-bar calculator supports...
Numi is a calculator that magically combines calculations with text, and allows you to freely share your computations. Numi combines text editor and calculator Support plain English. For example, '5... Read more
EtreCheck 3.3.3 - For troubleshooting yo...
EtreCheck is an app that displays the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to... Read more
BusyContacts 1.1.8 - Fast, efficient con...
BusyContacts is a contact manager for OS X that makes creating, finding, and managing contacts faster and more efficient. It brings to contact management the same power, flexibility, and sharing... Read more

Latest Forum Discussions

See All

The best new games we played this week
We were quite busy this week. A bunch of big mobile games launched over the past few days, alongside a few teeny surprises. There're lots of quality games to load your phone with. We've gone and picked out five of our favorites for the week. [... | Read more »
Magikarp Jump beginner's guide
Magikarp Jump is a mystifying little game. Part Tamagotchi, part idle clicker, there's not a whole lot of video game there, per se, but for some reason we can't help coming back to it again and again. Your goal is to train up a little Magikarp to... | Read more »
Goat Simulator PAYDAY (Games)
Goat Simulator PAYDAY 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICES **iPhone 4S, iPad 2, iPod Touch 5 or better Goat Simulator: Payday is the most... | Read more »
GRID Autosport delayed until autumn
Sorry mobile racing fans -- GRID Autosport has been delayed a few months. The game is now expected to launch this fall on iOS. Feral Interactive announced that they wanted more time to work on the game's UI and overall performance before launching... | Read more »
Zombie Gunship Survival Beginner's...
The much anticipated Zombie Gunship Survival is here. In this latest entry in the Zombie Gunship franchise, you're tasked with supporting ground troops and protecting your base from the zombie horde. There's a lot of rich base building fun, and... | Read more »
Mordheim: Warband Skirmish (Games)
Mordheim: Warband Skirmish 1.2.2 Device: iOS Universal Category: Games Price: $3.99, Version: 1.2.2 (iTunes) Description: Explore the ruins of the City of Mordheim, clash with other scavenging warbands and collect Wyrdstone -... | Read more »
Mordheim: Warband Skirmish brings tablet...
Legendary Games has just launched Mordheim: Warband Skirmish, a new turn-based action game for iOS and Android. | Read more »
Magikarp Jump splashes onto Android worl...
If you're tired ofPokémon GObut still want something to satisfy your mobilePokémon fix,Magikarp Jumpmay just do the trick. It's out now on Android devices the world over. While it looks like a simple arcade jumper, there's quite a bit more to it... | Read more »
Purrfectly charming open-world RPG Cat Q...
Cat Quest, an expansive open-world RPG from former Koei-Tecmo developers, got a new gameplay trailer today. The video showcases the combat and exploration features of this feline-themed RPG. Cat puns abound as you travel across a large map in a... | Read more »
Jaipur: A Card Game of Duels (Games)
Jaipur: A Card Game of Duels 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: ** WARNING: iPad 2, iPad Mini 1 & iPhone 4S are NOT compatible. ** *** Special Launch Price for a limited... | Read more »

Price Scanner via MacPrices.net

Memorial Day savings: 13-inch Touch Bar MacBo...
B&H Photo has the 2016 Apple 13″ Touch Bar MacBook Pros in stock today and on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 13″ 2.9GHz/512GB... Read more
Apple refurbished 13-inch MacBook Airs availa...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: - 13″ 1.6GHz/8GB/128GB MacBook Air: $... Read more
Apple restocks refurbished 11-inch MacBook Ai...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models recently discontinued by Apple), available for up to $170 off original MSRP. An Apple one-year warranty is included with each... Read more
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H has 12″ 1.2GHz Retina MacBooks on sale for up to $150 off MSRP. Shipping is free, and B&H charges NY & NJ sales tax only: - 12″ 1.2GHz Space Gray Retina MacBook: $1449.99 $150 off... Read more
15-inch 2.7GHz Silver Touch Bar MacBook Pro o...
MacMall has the 15-inch 2.7GHz Silver Touch Bar MacBook Pro (MLW82LL/A) on sale for $2569 as part of their Memorial Day sale. Shipping is free. Their price is $230 off MSRP. Read more
Free Tread Wisely Mobile App Endorsed By Fath...
Just in time for the summer driving season, Cooper Tire & Rubber Company has announced the launch of a new Tread Wisely mobile app. Designed to promote tire and vehicle safety among teens and... Read more
Commercial Notebooks And Detachable Tablets W...
Worldwide shipments of personal computing devices (PCDs), comprised of traditional PCs (a combination of desktop, notebook, and workstations) and tablets (slates and detachables), are forecast to... Read more
Best value this Memorial Day weekend: Touch B...
Apple has Certified Refurbished 2016 15″ and 13″ MacBook Pros available for $230 to $420 off original MSRP. An Apple one-year warranty is included with each model, and shipping is free: - 15″ 2.6GHz... Read more
13-inch MacBook Airs on sale for up to $130 o...
Overstock.com has 13″ MacBook Airs on sale for up to $130 off MSRP including free shipping: - 13″ 1.6GHz/128GB MacBook Air (sku MMGF2LL/A): $869.99 $130 off MSRP - 13″ 1.6GHz/256GB MacBook Air (sku... Read more
2.8GHz Mac mini available for $973 with free...
Adorama has the 2.8GHz Mac mini available for $973, $16 off MSRP, including a free copy of Apple’s 3-Year AppleCare Protection Plan. Shipping is free, and Adorama charges sales tax in NY & NJ... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
*Apple* Media Products - Commerce Engineerin...
Apple Media Products - Commerce Engineering Manager Job Number: 57037480 Santa Clara Valley, California, United States Posted: Apr. 18, 2017 Weekly Hours: 40.00 Job Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.