Beefy Boxes and Bandwidth Generously Provided by pair Networks
Welcome to the Monastery
 
PerlMonks  

Comment on

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

1) the open || die statement should actually be

open IN, $infile or die "Can't open input file: $!";
For reasons of precedence.

2) Here are some faster algorithms. One way is to use a hash to record which characters you've already placed into your substitution string. Here's the main loop:

my %set; my $substit = ""; for (1..26) { my $randchar; do { $randchar = chr((int rand 26) + 65) } while $set{$randchar}++; $substit .= $randchar; }
This way you don't have to do a search through the string each time.

And here's an even better way of doing it: build a random permutation of the alphabet string. To do this, we'll actually need an array:

my @alpha = split //, "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
Now we set another array equal to this one, then call the random shuffle algorithm on it:
my @crypt = @alpha; fisher_yates_shuffle(\@crypt);
which shuffles the array in place. Now all you need to do is get back the substitution string:
my $substit = join '', @crypt;
Here's the definition of the fisher_yates_shuffle sub:
sub fisher_yates_shuffle { my $array = shift; for (my $i = @$array; --$i; ) { my $j = int rand ($i+1); next if $i == $j; @$array[$i, $j] = @$array[$j, $i]; } return join '', @$array; }
(Taken directly from perlfaq4.)

I did some benchmarking on these, and here's what I got:

Benchmark: timing 5000 iterations of orig, f_yates, hash... orig: 33 secs (23.60 usr 0.00 sys = 23.60 cpu) f_yates: 5 secs ( 2.88 usr 0.00 sys = 2.88 cpu) hash: 13 secs ( 5.68 usr 0.00 sys = 5.68 cpu)
where "orig" is the one you posted, "f_yates" is the one using fisher_yates_shuffle, and "hash" is the one using a hash to record seen characters.

If I've messed anything up, let me know.


In reply to RE: Cryptogram Generator by btrott
in thread Cryptogram Generator by Elihu

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
  • Outside of code tags, you may need to use entities for some characters:
            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 2014-08-31 05:13 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The best computer themed movie is:











      Results (294 votes), past polls