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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 (Pope) 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;
Re^2: Algorithm for cancelling common factors between two lists of multiplicands
by BrowserUk (Pope) 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.
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      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

      Not quite the solution you asked for. Close enough?

      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

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