Multiplication is a commutative operation (a*b and b*a are the same quantity). That means that we can eliminate half of the operations making the inner J loop stop when $j becomes lesser than $i. You can see that explicit as the condition of the J loop.

Other trick used to trim the search space is taking into account that for natural numbers if a >= b then a*c >= b*c, so as soon as we found a $j that makes a palindrome we can stop the J loop.

Finally whatever becomes $prod <= $best we can also stop J; or even I if $j is still at 999.

In reply to Re^3: Largest palindrome number for a 3 digit product of 2 numbers by salva
in thread Largest palindrome number for a 3 digit product of 2 numbers by pr33

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.