comment on

If the solution in my earlier node doesn't return what you want, this surely will:

use Math::BigInt ();

*gcd = \&Math::BigInt::bgcd;

sub embiggen {
   local $_ = @_ ? $_[0] : $_;
   return Math::BigInt->new($_);
}


my @a = ( 10, 20, 33, 45, 60 );
my @b = ( 2, 5, 10, 12, 16, 23, 45 );


# my %a = map { $_ => 1 } @a;
# my %b = map { $_ => 1 } @b;
#
# my @c = map embiggen,
#         grep { !$b{$_} }
#         @a;
#
# my @d = map embiggen,
#         map { Math::BigInt->new($_) } 
#         grep { !$a{$_} }
#         @b;

my @c = @a;
my @d = @b;

foreach my $c (@c) {
   foreach my $d (@d) {
      my $gcd = gcd($c, $d);
      $c /= $gcd;
      $d /= $gcd;
   }
}

@c = grep { $_ != 1 } @c;
@d = grep { $_ != 1 } @d;
[download]

or this messier but potentially faster alternative:

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

*gcd    = \&Math::BigInt::bgcd;
*factor = \&Math::Big::Factors::factors_wheel;

sub embiggen {
   local $_ = @_ ? $_[0] : $_;
   return Math::BigInt->new($_);
}


my @a = ( 10, 20, 33, 45, 60 );
my @b = ( 2, 5, 10, 12, 16, 23, 45 );


# my %a = map { $_ => 1 } @a;
# my %b = map { $_ => 1 } @b;
#
# my @c = map embiggen,
#         grep { !$b{$_} }
#         @a;
#
# my @d = map embiggen,
#         grep { !$a{$_} }
#         @b;

my @c = @a;
my @d = @b;


my %c_factors;

foreach my $c_idx (0..$#c) {
   my @c_factors = factor($c[$c_idx]);
   foreach my $c_factor (@c_factors) {
      push(@{$c_factors{$c_factor}}, $c_idx);
   }
}


foreach my $d (@d) {
   my @d_factors = factor($d);
   foreach my $d_factor (@d_factors) {
      next unless $c_factors{$d};
      next unless @{$c_factors{$d}};

      my $c_idx = shift(@{$c_factors{$d}});
      $c[$c_idx] /= $d_factor;
      $d         /= $d_factor;
   }
}


@c = grep { $_ != 1 } @c;
@d = grep { $_ != 1 } @d;
[download]

Both untested.

In reply to Re^2: Algorithm for cancelling common factors between two lists of multiplicands by ikegami
in thread Algorithm for cancelling common factors between two lists of multiplicands by BrowserUk

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