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in reply to Algorithm for cancelling common factors between two lists of multiplicands

If the arrays don't contain duplicate elements:

$c{$_}++ foreach @a;
$c{$_}++ foreach @b;

@c = grep { $c{$_} != 2 } @a;
@d = grep { $c{$_} != 2 } @b;

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Re^2: Algorithm for cancelling common factors between two lists of multiplicands
by ikegami (Patriarch) on Aug 08, 2005 at 19:49 UTC

    This works whether the arrays contain duplicate elements or not:

    my %a = map { $_ => 1 } @a;
my %b = map { $_ => 1 } @b;

@c = grep { !$b{$_} } @a;
@d = grep { !$a{$_} } @b;

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[d/l]
Re^2: Algorithm for cancelling common factors between two lists of multiplicands
by BrowserUk (Patriarch) on Aug 08, 2005 at 19:50 UTC

    Please look again. This is not the elimination of duplicates.

    Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
    Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
    "Science is about questioning the status quo. Questioning authority".
    The "good enough" maybe good enough for the now, and perfection maybe unobtainable, but that should not preclude us from striving for perfection, when time, circumstance or desire allow.
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[d/l]
      oops, you're right. I can't figure out what the pattern is. What does he mean by "canceling out"?

      Update: Here's a solution:

      use Math::BigInt       ();
use Math::Big::Factors ();

my $a = Math::BigInt->new(1);
$a *= $_ foreach @a;  # 17820000

my $b = Math::BigInt->new(1);
$b *= $_ foreach @b;  # 19872000

my $gcd = Math::BigInt::bgcd($a, $b);  # 108000

my $c = $a / $gcd;  # 165
my $d = $b / $gcd;  # 184

my @c = Math::Big::Factors::factors_wheel($c);  # 3, 5, 11
my @d = Math::Big::Factors::factors_wheel($d);  # 2, 2, 2, 23

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      Not quite the solution you asked for. Close enough?

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[d/l]

      Is this a factoring problem? Math::Factor and Math::Big::Factors may have useful routines. In particular Math::Factor has the subroutine "match" that sounds something like what you're trying to do, though as others have stated, it's still not clear what exactly that is.

      -xdg

      Code written by xdg and posted on PerlMonks is public domain. It is provided as is with no warranties, express or implied, of any kind. Posted code may not have been tested. Use of posted code is at your own risk.

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