And for the file: 
2
2
2
3
3
3
4
4
5
How would that be handled? 
this    or  that?
2             2
3             3
4             2
5             3
2             4
3             2
4             3
2             4
3             5
Fundamentaly whay you need is this: 
# Create an array of numbers with values...
my %numbers = ();
for (<FILE>){
   chomp;
   $numbers{$_}++; # tally the occurences of numbers..
   # Could add a preemptive 'last' if numbers not contiguous
}

while( %numbers ){
  # satisfies "this" criteria, insert a reverse for "that"
  for ( sort keys %numbers ){
    print "$_\n";
    delete $numbers{$_} unless --$numbers{$_};
    # Add a routine here to remove all higher values
    # and warn if numbers are non-contiguous.
  }
}

[download]
If this is homework, please note we're not here to do your thinking for you, just to help you think in Perl.

--

Brother Frankus.

¤

In reply to Re: Text Manipulation Quickie by frankus
in thread Text Manipulation Quickie by johnirl

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!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • 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, details, 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, summary, 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.