TweetFollow Us on Twitter

Apr 94 Challenge
Volume Number:10
Issue Number:4
Column Tag:Programmers’ Challenge

Related Info: Memory Manager

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.

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 (i.e., don’t use Think’s Object extensions). Only pure C code can be used. Any entries with any assembly in them will be disqualified (except for those challenges specifically stated to be in assembly). However, you may call any routine in the Macintosh toolbox you want (i.e., it doesn’t matter if you use NewPtr instead of malloc). 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. All code should be limited to 60 characters wide. This will aid us in dealing with e-mail gateways and page layout.

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:, CompuServe: 71552,174 and America Online: MT PRGCHAL. 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.


This month’s challenge is to swap two adjacent blocks of memory using a finite amount of temporary swap space. This is something the Memory Manager has to do quite often as it shuffles blocks around in the heap.

The prototype of the function you write is:

/* 1 */
void SwapBlocks(p1, p2, swapPtr size1,
  size2, swapSize)
void    *p1;
void    *p2;
void    *swapPtr;
unsigned long  size1;
unsigned long  size2;
unsigned long  swapSize;

p1 and p2 point to the beginnings of the two blocks to swap. size1 and size2 are their respective sizes (in bytes). Both blocks begin on addresses divisible by 4 and have sizes that are divisible by 4. swapPtr points to the scratch area you can use (if you need to) and swapSize is the size of that area (between 256 and 4096 bytes, inclusive). swapPtr and swapSize are also each divisible by 4. If the two blocks look like this on entry:

/* 2 */
^       ^
p1      p2    size1 = 8   size2 = 12

then the same memory locations will look like this on exit:

/* 3 */

When measuring performance I will be calling your routine many times. The distribution of the sizes of the blocks is as follows:

4 to 16 bytes 20% of the time

20 to 32 bytes 20% of the time

36 to 64 bytes 20% of the time

68 to 256 bytes 20% of the time

260 to 4096 bytes 10% of the time

4100 or more bytes 10% of the time

You would normally write this kind of routine in assembly, but let’s see how well you can do in pure C (remember, everyone has the same handicap). If you want to submit a pure assembly solution along with your pure C solution then please do so (but the assembly version will NOT be counted as an entry in the challenge and it will not win anything other than a mention in this column).


Of the 11 entries I received for the We Pry Any Heap (Happy New Year) anagram challenge, only 5 worked correctly. Congrats to Larry Landry (Rochester, NY) for the dual honor of coming in 1st both in terms of speed and smallest code size.

The times for anagramming “programmer” (462 anagrams) and “mactech magazine” (3365 anagrams) with a 19,335 word English dictionary are given here (more weight was given to longer inputs (15-30 characters) when ranking contestants). Numbers in parens after a person’s name indicate how many times that person has finished in the top 5 places of all previous Programmer Challenges, not including this one:

Name code time 1 time 2

Larry Landry (1) 830 20 1048

Stepan Riha (5) 2352 45 1166

Bob Boonstra (6) 1370 52 1688

Allen Stenger (3) 1044 23 1701

Mark Nagel 1134 81 51407

Most of the entrants figured out that the key to speeding up the anagram process was to pare down the size of the dictionary first. Once you have the input characters you can eliminate any word in the dictionary that: (1) contains more characters than the input, (2) contains at least one letter not in the input set or, (3) contains more of any particular character than the input. For instance, if your input is “programmer” then you can remove any word in the dictionary that (1) is more than 10 characters long, (2) is not made up entirely of the letters [p, r, o, g, a, m, e] and, (3) contains more than any one of: 1 p, 3 r’s, 1 o, 1 g, 1 a, 2 m’s, or 1 e.

Stepan Riha (Austin, TX) took this “reduce the dictionary” idea one step further and came up with a way to store words that are permutations of each other (like ‘stop’, ‘post’ and ‘pots’) as one entry in the dictionary (and when it’s time to output an anagram he outputs all permutations for each word in the output).

Several people wrote to me and asked if reordering the words in each output anagram was necessary (i.e. ‘pale rain’ and ‘rain pale’). I admit that it wasn’t clear in the puzzle specification exactly what qualified as a ‘unique’ anagram so I allowed either interpretation. The only one of the 5 correct entries that did count word reorderings as unique anagrams is Mark Nagel (Irvine, CA) and his times above reflect that fact.

Here’s Larry’s winning solution:

Anagram Programmer's Challenge

by Larry Landry

This implementation uses a large amount of memory to optimize the CPU utilization. To guarantee that we have enough memory for all matching words, we actually allocate an array of pointers for 30,000 words. Since the rules stated that there would be about 20,000 words in the dictionary, even if every word matched, we would still have enough storage. In reality this number could probably be less than 1-200 for all but the most rare of scenarios.

The basic algorithm is: 1) Convert the input string into a table of counts for each character from a-z. So "sammy" would have a count of 2 for "m" and 1 for each of "s", "a", and "y". This makes testing for the presence of a character as simple as checking and indexed value in an array. 2) Parse through the dictionary and find the words that can be composed of some portion of characters from the input characters. Build a list of pointers to each word. The number of words in this list will be in the tens instead of thousands. 3) Recursively process the words in this list and find strings of words that use up all of the characters. For each matching sequence, output the words to the file. The processing required by this algorithm is then

D * C1 + M * log2(M) * C2


D = size of input dictionary

M = number of matching words

C1 & C2 are constants

This algorithm works very well for cases where there are few words that match the input letters. The worst case scenario where all words can be made from the input letters will still take a very long time. I expect that matching words will typically be less than 100.

/* 4 */
#include   <stdio.h>

typedef unsigned char   uchar;
typedef unsigned short ushort;
typedef unsigned long  ulong;

#define MAX_WORDS   30000L
#define OUTPUT_BUFFER_SIZE  10000L
#define RETURN  '\n'

typedef struct {
   short   fWordLength;
} WordLoc;

/* Usage counts for each character (only indexes 'a' to 'z' are actually 
used) */
typedef uchar   CharData[256];

unsigned long Anagram(Str255 inputText, FILE *wordList,
   FILE *outputFile);

ulong findInputWords(register char *wordBuffer,
   WordLoc *validWords);
ulong findAnagrams(short numValidChars, ulong wordCount,
   WordLoc *validWords, short prevWordCount);

/* I use some global variables here to avoid passing them down into the 
recursive routine findAnagrams().  These values are constant once findAnagrams() 
is called. */

char     gOutputBuffer[OUTPUT_BUFFER_SIZE];
char    *gOutputBufferEnd = gOutputBuffer + 
char    *gOutputPtr;
CharData  gValidChars;
WordLoc  *gWordsInUse[255];
FILE    *gOutputFile;

unsigned long Anagram(Str255 inputText, FILE *wordList,
   FILE *outputFile)
   fpos_t  wordBufferLength;
   char*  wordBuffer;
   short   index;
   short   numValidChars;
   WordLoc validWords[MAX_WORDS];
   char   ch;
   ulong   wordCount;

   gOutputFile = outputFile;
   gOutputPtr = gOutputBuffer;

/* To save on file I/O time, read the whole file all at once.  First, 
find the length of the file by seeking the end and finding the file pos. 
 Then allocate a buffer of that size, plus 2 bytes  (for a return and 
NULL char) and read the data into it.  Finally put the return and NULL 
char at the end. */

   fseek(wordList, 0L, SEEK_END);
   fgetpos(wordList, &wordBufferLength);
   wordBuffer = (char*) NewPtr((Size) wordBufferLength + 2);
   if (wordBuffer == NULL)
   return 0L;  /* real error handling here */
   fread(wordBuffer, (size_t) 1,
   (size_t) wordBufferLength, wordList);
   if (wordBuffer[wordBufferLength-1] != RETURN)
   wordBuffer[wordBufferLength++] = RETURN;
   wordBuffer[wordBufferLength] = '\0';

/* To save time ruling out words, we build a list of the valid characters 
in the words.  We start with no valid characters. */
   for (index='a'; index<'z'; index++)
   gValidChars[index] = 0;

/* Now build the list of valid characters.  Each array entry will be 
a count of how many times that character is present. */
   numValidChars = *inputText++;
   for (index=numValidChars; index>0; index--)
   if ((ch = *inputText++) != ' ')
/* Find the list of words that can be made up from the letters in the 
input word */
   wordCount = findInputWords(wordBuffer,
/* Now find the list of full anagrams that can be created from these 
words */
   wordCount = findAnagrams(numValidChars, wordCount,
   &validWords[MAX_WORDS-wordCount], 0);
/* Write the results to the output */
   *gOutputPtr = 0;/* Terminate the string */
   fprintf(outputFile, gOutputBuffer);
   return wordCount;
} /* Anagram */

ulong findInputWords(register char *wordBuffer,
   WordLoc *validWords)
   char*saveStart = wordBuffer;
   ulong   numberWords = 0;
   char ch;

   while (*wordBuffer)
   ch = *wordBuffer++;
   if (ch == RETURN)
/* Record this entry as a valid word */
   validWords->fWordStart = saveStart;
   validWords->fWordLength = (short)(wordBuffer -
   saveStart - 1);

   while (saveStart < wordBuffer)

/* Save the new start of word pointer */
   saveStart = ++wordBuffer;
   } else if (gValidChars[ch])
/* This word didn't match so reset and go to the next word */
   while (saveStart < wordBuffer)
   while (*wordBuffer++ != RETURN)
/* Save the new start of word pointer */
   saveStart = wordBuffer;
   } /* else */
   } /* while */
   return numberWords;
} /* findInputWords */

ulong findAnagrams(short numValidChars, ulong wordCount,
   WordLoc *validWords, short prevWordCount)
   ulong   wordIndex;
   ulong   usedIndex;
   short   chIndex;
   ulong   matchCount = 0;
   Boolean wordFits;
   char ch;
   WordLoc *theWord;

/* Try each word we have against the list of characters. */
   for (wordIndex=0; wordIndex<wordCount; wordIndex++)
/* If there aren't enough characters left,  it can't be a match */
   if (validWords->fWordLength <= numValidChars)
/* Go through the chars in this word testing to make sure that there 
is at least one of each char  available */
   wordFits = TRUE;
   for (chIndex=0; chIndex<validWords->fWordLength; chIndex++)
   ch = validWords->fWordStart[chIndex];
   if (gValidChars[ch])
/* Found an unavailable character, so this can't be part of the anagram. 
 Reset the character usage array and go to the next word. */
   wordFits = FALSE;
   while (--chIndex >= 0)
   break;  /* get out of the for loop */
   } /* else */
   } /* for */

   if (wordFits)
/* This word fit, so see if it uses all the characters.   If so, then 
we have found an anagram.  Output the  anagram and increment the anagram 
count. */
   if (validWords->fWordLength == numValidChars)
/* Copy the previous words for this anagram separated by spaces. */
   for (usedIndex=0; usedIndex<prevWordCount; usedIndex++)
   theWord = gWordsInUse[usedIndex];
   memcpy(gOutputPtr, theWord->fWordStart,
   (size_t) theWord->fWordLength);
   gOutputPtr += theWord->fWordLength;
   *gOutputPtr++ = ' ';
   } /* for */
/* Now copy this new word and a return character */
   memcpy(gOutputPtr, validWords->fWordStart,
   (size_t) validWords->fWordLength);
   gOutputPtr += validWords->fWordLength;
   *gOutputPtr++ = RETURN;

/* To ensure that we don't overrun the output buffer check against the 
end of the buffer.  If the end pointer has been passed, write the data 
to the file  and reset the output pointer to the beginning of the buffer. 
   if (gOutputPtr > gOutputBufferEnd)
 *gOutputPtr = 0;/* Terminate the string */
   fprintf(gOutputFile, gOutputBuffer);
   gOutputPtr = gOutputBuffer;
   } /* if */
   }  /* if */
/* This word did fit, but didn't use all of the characters so add it 
to the list of previous words  in the anagram and then call this procedure 
recursively to find if there are more words that can be added to make 
an anagram with this base. */
   gWordsInUse[prevWordCount] = validWords;
   matchCount += findAnagrams(
   numValidChars - validWords->fWordLength,
   wordCount - wordIndex, validWords,
   prevWordCount + 1);
   } /* else */

/* Now undo the characters we took out of the validChar array */
   for (chIndex=0;chIndex<validWords->fWordLength;chIndex++)
   } /* if */
   } /* if */

 } /* for */

   return matchCount;
} /* findAnagrams */


Community Search:
MacTech Search:

Software Updates via MacUpdate

Shimo - VPN client – for everyon...
Shimo is the most versatile VPN client for OS X and it enables really everybody to master secure network. It supports more protocols than any other VPN application out there! CiscoVPN, AnyConnect,... Read more
Dash 3.4.0 - Instant search and offline...
Dash is an API documentation browser and code snippet manager. Dash helps you store snippets of code, as well as instantly search and browse documentation for almost any API you might use (for a full... Read more
AirRadar 3.1.9 - $9.95
With AirRadar, scanning for wireless networks is now easier and more personalized! It allows you to scan for open networks and tag them as favourites or filter them out. View detailed network... Read more
Printopia 2.1.22 - Share Mac printers wi...
Run Printopia on your Mac to share its printers to any capable iPhone, iPad or iPod Touch. Printopia will also add virtual printers, allowing you to save print-outs to your Mac and send to apps.... Read more
SteerMouse 5.0 - Powerful third-party mo...
SteerMouse is an advanced driver for USB and Bluetooth mice. It also supports Apple Mighty Mouse very well. SteerMouse can assign various functions to buttons that Apple's software does not allow,... Read more
Alarm Clock Pro 10.2.5 - $19.95
Alarm Clock Pro isn't just an ordinary alarm clock. Use it to wake you up in the morning, send and compose e-mails, remind you of appointments, randomize the iTunes selection, control an internet... Read more
Cocktail 10.1 - General maintenance and...
Cocktail is a general purpose utility for macOS that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
RapidWeaver 7.1.7 - Create template-base...
RapidWeaver is a next-generation Web design application to help you easily create professional-looking Web sites in minutes. No knowledge of complex code is required, RapidWeaver will take care of... Read more
MacCleanse 5.1.6 - $29.95
MacCleanse is the product of thousands of hours of intense research and development. It meticulously scans all of the nooks and crannies of a computer for unnecessary junk that can take up huge... Read more
Slack 2.3.0 - Collaborative communicatio...
Slack is a collaborative communication app that simplifies real-time messaging, archiving, and search for modern working teams. Version 2.3.0: Note: Now requires OS X 10.8 or later New The app... Read more

Latest Forum Discussions

See All

4 addictive clicker games like Best Fien...
Clickers are passive games that take advantage of basic human psychology to suck you in, and they're totally unashamed of that. As long as you're aware that this game has been created to take hold of your brain and leave you perfectly content to... | Read more »
Smile Inc. Guide: How not to die on the...
As if Mondays weren't bad enough, at Smile Inc. you have to deal with giant killer donuts, massive hungry staplers, and blasting zones. It's not exactly a happy, thriving work environment. In fact, you'll be lucky to survive the nine to five.... | Read more »
Oh...Sir! The Insult Simulator (Games)
Oh...Sir! The Insult Simulator 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: | Read more »
WitchSpring2 (Games)
WitchSpring2 1.27 Device: iOS Universal Category: Games Price: $3.99, Version: 1.27 (iTunes) Description: This is the story of Luna, the Moonlight Witch as she sets out into the world. This is a sequel to Witch Spring. Witch Spring 2... | Read more »
4 popular apps getting a Halloween makeo...
'Tis the season for all things spooky. So much, so, in fact, that even apps are getting into the spirt of things, dressing up in costume and spreading jack o' lanterns all about the place. These updates bring frightening new character skins, scary... | Read more »
Pokémon GO celebrates Halloween with can...
The folks behind Pokémon GO have some exciting things planned for their Halloween celebration, the first in-game event since it launched back in July. Starting October 26 and ending on November 1, trainers will be running into large numbers of... | Read more »
Best Fiends Forever Guide: How to collec...
The fiendship in Seriously's hit Best Fiends has been upgraded this time around in Best Fiends Forever. It’s a fast-paced clicker with lots of color and style--kind of reminiscent of a ‘90s animal mascot game like Crash Bandicoot. The game... | Read more »
5 apps for the budding mixologist
Creating your own cocktails is something of an art form, requiring a knack for unique tastes and devising interesting combinations. It's easy to get started right in your own kitchen, though, even if you're a complete beginner. Try using one of... | Read more »
5 mobile strategy games to try when you...
Strategy enthusiasts everywhere are celebrating the release of Civilization VI this week, and so far everyone seems pretty satisfied with the first full release in the series since 2010. The series has always been about ultra-addictive gameplay... | Read more »
Popclaire talk to us about why The Virus...
Humanity has succumbed to a virus that’s spread throughout the world. Now the dead have risen with a hunger for human flesh, and all that remain are a few survivors. One of those survivors has just called you for help. That’s the plot in POPCLAIRE’... | Read more »

Price Scanner via

13-inch 2.5GHz MacBook Pro (Apple refurbished...
Apple has Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros... Read more
Apple refurbished 2015 13-inch MacBook Airs a...
Apple has Certified Refurbished 2015 13″ MacBook Airs available starting at $759. An Apple one-year warranty is included with each MacBook, and shipping is free: - 2015 13″ 1.6GHz/4GB/128GB MacBook... Read more
64GB Apple TV on sale for $159, save $40
Best Buy has the 64GB Apple TV on sale for $40 off MSRP on their online store. Choose free shipping or free local store pickup (if available). Sale price for online orders only, in-store price may... Read more
EyeQue Introduces iOS And Android Based Advan...
Affordable vision technologies developers EyeQue have announced what they claim to be the world’s most advanced intelligent vision solution, pitched as enabling anyone, anywhere to easily and... Read more
Smartwatch Market Tanks, Declining 51.6% in 2...
The worldwide smartwatch market experienced a round of growing pains in the third quarter of 2016 (3Q16), resulting in a year-over-year decline in shipment volumes. According to data from the... Read more
CAZE announces Ultra Thin Glass Screen Protec...
Hong Kong based CAZE has announced its first ultra thin glass screen protector, the Glazz Pro for iPhone 7/7 Plus. Glazz Pro is made from chemically reinforced glass with an anti-fingerprint... Read more
11-inch MacBook Airs on sale for up to $120 o...
Newegg has 11″ MacBook Airs on sale for up to $120 off MSRP. Shipping is free: - 11″ 1.6GHz/128GB MacBook Air: $799.99 $100 off MSRP - 11″ 1.6GHz/256GB MacBook Air: $979 $120 off MSRP Read more
Up to $300 off Macs, $20 off iPads with Apple...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free, and... Read more
Apple’s Thursday “Hello Again” Event A Largel...
KGI Securities analyst Ming-Chi Kuo, who has a strong record of Apple hardware prediction accuracy, forecasts in a new note to investors released late last week that a long-overdue redo of the... Read more
12-inch Retina MacBooks on sale for $100 off...
Amazon has 2016 12″ Apple Retina MacBooks on sale for $100 off MSRP. Shipping is free: - 12″ 1.1GHz Silver Retina MacBook: $1199.99 $100 off MSRP - 12″ 1.1GHz Gold Retina MacBook: $1199.99 $100 off... Read more

Jobs Board

Security Data Analyst - *Apple* Information...
…data sources need to be collected to allow Information Security to better protect Apple employees and customers from a wide range of threats.Act as the subject 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* Solutions Consultant - Apple (United...
# Apple Solutions Consultant Job Number: 52812872 Houston, Texas, United States Posted: Oct. 18, 2016 Weekly Hours: 40.00 **Job Summary** As an Apple Solutions Read more
Lead *Apple* Solutions Consultant - Apple (...
# Lead Apple Solutions Consultant Job Number: 52812906 Houston, Texas, United States Posted: Oct. 18, 2016 Weekly Hours: 40.00 **Job Summary** The Lead ASC is an Read more
*Apple* Retail - Multiple Positions- Towson,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.