comment on

for my $i (1..$#a) {
  my $random= rand( $i);
  swap(\$a[$i], \$a[$random]);
}
[download]

Since any position is only swapped once with any of the previous places, there can't be the initial value in any place. But still any value can go to any other position in the array. Per induction I think I can show that the values are equally distributed.

EDIT: Thanks Joost, I was too sloppy, even used { instead of [. If I remember correctly it would work without the \ since @_ in the sub is an alias to the parameters, but this way the side effect is more obvious

In reply to Re: Random Derangement Of An Array by jethro
in thread Random Derangement Of An Array by Limbic~Region

Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
Want more info? How to link or How to display code and escape characters are good places to start.


Pathologically Eclectic Rubbish Lister
	PerlMonks