Beefy Boxes and Bandwidth Generously Provided by pair Networks
good chemistry is complicated,
and a little bit messy -LW
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

Recently, the C# programmers at work have been asking job applicants to write a function to reverse a string of words. For example, given an input string of:

" one two three four "
the function should produce:
"four three two one"
That is, the input string reversed word by word, with a single space between each word and with no leading or trailing space. You may assume the input string consists only of alphabetic characters, spaces and tabs.

A popular C# approach goes something like:

private static string reverseWords(string str) { string[] words = Array.FindAll<string>(str.Split( new char[] {' ','\t'}), delegate(string s) { return !String.IsNullOrEmpty(s); }); int i = words.Length - 1; if (i < 0) return String.Empty; StringBuilder sb = new StringBuilder(words[i]); while (--i >= 0) sb.Append(' ').Append(words[i]); return sb.ToString(); }
Though the C# programmers seemed happy with this solution, it's a bit too verbose for my personal taste. When I suggested replacing all the StringBuilder claptrap with:
Array.Reverse(words); return String.Join(" ", words);
they surprised me by saying they preferred the former version because StringBuilder was "faster" (though I couldn't measure any significant difference in running time).

Anyway, this little episode provoked me into solving their little problem in other, er, less verbose languages.

In Perl 5, I whipped up:

sub reverseWords { join ' ', reverse split(' ', shift) }
after a few seconds thought, then pondered a Perl 6 version:
sub reverseWords(Str $s) returns Str { $s.words.reverse.join(' ') }
which resembles a Ruby version:
def reverseWords(s) s.split.reverse.join(' ') end
Finally, this Haskell version:
reverseWords = unwords . reverse . words
may well be the winner of a multi-language golf competition. ;-)

Though one artificial little program proves nothing, at least I've had the satisfaction of demonstrating that this little problem can be easily solved as a one liner in many languages.

Please feel free to improve any of these solutions and/or add a new version in a language of your choice.

References

Acknowledgements: I'd like to thank the friendly folks at Haskell-Cafe for helping me with the Haskell version.

Updated 13-dec: Changed from split to comb in accordance with latest S29, which specifies that split no longer has a default delimiter and advises you instead to comb the words out of the string when splitting on whitespace. Updated 6-oct-2008: Added References section. Updated 10-0ct-2010. Changed comb to words, thanks moritz.


In reply to Five Ways to Reverse a String of Words (C#, Perl 5, Perl 6, Ruby, Haskell) by eyepopslikeamosquito

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others about the Monastery: (5)
    As of 2015-07-30 00:25 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The top three priorities of my open tasks are (in descending order of likelihood to be worked on) ...









      Results (269 votes), past polls