#! perl -slw
use strict;
use List::Util qw[ sum shuffle ];

for (
    [ 22, 27, 57],
    [ 11, 62, 39],
) {
    my( $a1, $a2 ) = partition( 30, $_ );
    my( $t1, $t2 ) = ( sum( @$a1), sum( @$a2 ) );
    print "\n@$a1 := ", $t1;
    print "@$a2 := ", $t2;
    print "Diff: ", abs( $t1 - $t2 );
}



sub partition {
    my( $limit, $aRef ) = @_;
    my @in = sort{ $a <=> $b } @$aRef;
    my $target = sum( @in ) >> 1;
    my( $best, @best ) = 9e99;
    my $soFar = 0;
    my @half;
    for( 1 .. $limit ) {
#        printf "%6d : [@half] [@in] [@best]\n", abs( $soFar - $target
+ ) if $V;

        $soFar += $in[ 0 ], push @half, shift @in while $soFar < $targ
+et;
        return( \@half, \@in ) if $soFar == $target;

        my $diff = abs( $soFar - $target );
        ( $best, @best ) = ( $diff, @half ) if $diff < $best;

        $soFar -= $half[ 0 ], push @in, shift @half while $soFar > $ta
+rget;
        return( \@half, \@in ) if $soFar == $target;

        $diff = abs( $soFar - $target );
        ( $best, @best ) = ( $diff, @half ) if $diff < $best;

        srand( $_ );
        shuffle @in;
    }
    my %seen; $seen{ $_ }++ for @best;
    return \@best, [ grep{ --$seen{ $_ } < 0 } @$aRef ];
}
[download]

Update: I know know why the problem didn't show up in my version of the script. As I mentioned, I'm using a custom shuffle routine, which does an in-place shuffle. The List::Util version of shuffle is not in-place, hence the last line of the for loop should be @in = shuffle @in; for use with List::Util, not shuffle @in; as for my version. I've update the code below.

I apologise. It is a legit bug. I'm amazed it hasn't shown up before and confused as to why it doesn't show up in my lightly modified version of the same script you posted, but...this fixes it. Till the next one....

sub partition {
    my( $limit, $aRef ) = @_;
    my @in = sort{ $a <=> $b } @$aRef;
    my $target = sum( @in ) >> 1;
    my( $best, @best ) = 9e99;
    my $soFar = 0;
    my @half;
    for( 1 .. $limit ) {
#        printf "%6d : [@half] [@in] [@best]\n", abs( $soFar - $target
+ );

        $soFar += $in[ 0 ], push @half, shift @in
            while @in > 1 and $soFar < $target;
        return( \@half, \@in ) if $soFar == $target;

        my $diff = abs( $soFar - $target );
        ( $best, @best ) = ( $diff, @half ) if $diff < $best;

        $soFar -= $half[ 0 ], push @in, shift @half
            while @half > 1 and $soFar > $target;
        return( \@half, \@in ) if $soFar == $target;

        $diff = abs( $soFar - $target );
        ( $best, @best ) = ( $diff, @half ) if $diff < $best;

        srand( $_ );
        @in = shuffle @in;
        ## shuffle @in; ## Only works for an inplace shuffle!
    }
    my %seen; $seen{ $_ }++ for @best;
    return \@best, [ grep{ --$seen{ $_ } < 0 } @$aRef ];
}
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

Thank you so much BrowserUk!

It's working so far in a relatively small number of arrays (1000).
I already found one script that's giving me no error in tens of thousands on arrays. You can get it from the conversation, posted by 'tilly'.

For now I think I'll stick to that one. But after two days of trying everything I found here, I believe I must try yours together with tilly's and see if both of you have reached the same nirvana.
Just for the heck of being able to thank everyone that helped, and post a couple of scripts that work undeniably well.

My most sincere thanks.

Pepe