March 1996 Programmer's Challenge

Words The Reverse

Mail solutions to: progchallenge@mactech.com

Due Date: 10 March 1996

Text input, of Block given a in words of order the place (in reverse) will that routine a write to is challenge the month this. Oops, what I meant to say was: This month, the Challenge is to write a routine that will reverse (in place) the order of words in a given block of input text. The prototype for the code you should write is:

pascal void ReverseTheWords(
  const char *text,      /* the words you should reverse */
  const long numCharsIn  /* length of inputText in chars */
);
 

Specifically, ReverseTheWords should exchange the first word in the input text with the last word, the second word with the next-to-last word, etc. For the purpose of this Challenge, a word is defined as a continuous sequence of alphanumeric characters [a..zA..Z0..9]. Any nonalphanumeric characters should remain in their original positions and in their original order with respect to the new words; that is, punctuation, white space, and other characters between the first and second input words should, on output, be located between the new first and second words. As an example, ReverseTheWords would convert:

  This, however, <-is-> a (difficult) test.
 

into

  Test, difficult, <-a-> is (however) this.
 

As you can see from the example, there is one additional requirement. Your code needs to adjust the capitalization of words so that the n-th word is capitalized on output only if the n-th word was capitalized in the input text.

There are no specific restrictions on the amount of auxiliary memory you may use (within reason), so you may allocate a few buffers of size numCharsIn should you need them. Remember, however, to deallocate any memory you allocate before returning, as I will be calling your code many times.

Note that the prototype specifies the use of Pascal calling conventions. That is because this month we are conducting ...

A Language Experiment

Over the past months, in response to suggestions from readers, we have made a number of changes to the Challenge, including migrating to PowerPC native code and expanding to other C compilers. Now we are experimenting with some additional changes. This month, for the first time, your solution to the Challenge can be coded in C, C++, or Pascal, using your choice among the MPW, Metrowerks, or Symantec compilers for these languages. Although either 68K or PowerPC code is permitted, I will be running your code on a PowerMac 8500, so native code is obviously recommended. The environment you choose must support linking your solution with test code written in C. Along with your solution, you should specify the intended environment, compiler and compiler options, or (better yet) provide a project file or make file that will generate a stand-alone application that calls your solution from C test code.

Post-Publication Clarification

The published problem did not indicate how to capitalize the output when the input contains a word that starts with a numeric character. For example, "Catch 22." could be converted to "22 Catch." or to "22 catch.". Because the published problem statement was silent on how to deal with this case, either approach will be considered correct.

If you have any questions, please send me e-mail at one of the Programmer's Challenge addresses, or directly to boonstra@ultranet.com.

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Last modified by Bob Boonstra on 3/21/96.