Today's post "Find combination of numbers whose sum equals X" got me wondering about this: what's the "best" (= fastest, most memory-efficient, etc.) way to implement a (typically recursive) "pick without replacement" algorithm like this? Here's an example with splice, plus grepping the indicies, as choroba used here. Who has more ideas?

use warnings;
use strict;
use Benchmark qw/cmpthese/;

my @numbers = ( 0..20 );
my $index = 3;
my @expect = ( 0..2,4..20 );
use constant TEST => 0;

cmpthese(-2, {
    splice => sub {
        my @output = @numbers;
        splice @output, $index, 1;
        join("\0", @output) eq join("\0", @expect) or die if TEST;
    },
    grep => sub { # https://www.perlmonks.org/?node_id=11123877
        my @output = @numbers[ grep $_ != $index, 0 .. $#numbers ];
        join("\0", @output) eq join("\0", @expect) or die if TEST;
    },
});

__END__

            Rate   grep splice
grep    835107/s     --   -68%
splice 2575950/s   208%     --

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In reply to Fastest way to "pick without replacement" by haukex

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