Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl: the Markov chain saw
 
PerlMonks  

Comment on

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

It should be noted that many algorithm's O time can be reduced. For instance, many O(n^2) algorithms can be reduced to O(n log(n)) by finding a way to cut the inner loop short. A famous example is bubblesort:

# O(n^2) for my $i (0..$#a-1) { for (0..$#a-1-$i) { ($a[$_],$a[$_+1]) = ($a[$_+1],$a[$_]) if ($a[$_+1] < $a[$_]); } } # O(n log(n)) for my $i (0..$#a-1) { # looping over already-sorted items is not needed for (0..$#a-1-$i) { ($a[$_],$a[$_+1]) = ($a[$_+1],$a[$_]) if ($a[$_+1] < $a[$_]); } }

O(n) algorithms that involve a search via a loop can sometimes be reduced from O(n) to O(log(n)) by breaking out of the loop once a "result" is found:

# O(n) my $truestatus; foreach my $item (@list) { $truestatus = 1 if (some_condition); } # O(log(n)) my $truestatus; foreach my $item (@list) { # if some_condition is going to be valid for at least one $item in # @list, then the limit of the average runtime will approach # O(log n). if (some_condition) { $truestatus = 1; last } }

Of course, the secret is to know where to apply these optimizations, which is often harder than it seems :)


In reply to Re: An informal introduction to O(N) notation by jryan
in thread An informal introduction to O(N) notation by dws

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 surveying the Monastery: (10)
    As of 2014-08-28 06:24 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      The best computer themed movie is:











      Results (257 votes), past polls