Nice comparison. Your problem is basically testing for set membership, and that is often done using a hash if there are lots of searches:

use Benchmark qw(:all) ;

my $test_element = 42_000;
my @a = (1..100_000);

my $count = 20;
cmpthese($count, {
                  'hash' => sub {
                     my %seen;
                     undef( @seen{ @a } );  # a trick I learned from t
+illy
                     my $found = 0;
                     for my $iter (10_000..10_100) { # 101 searches
                        $found = 1 unless exists $seen{ $iter };
                     }
                     return $found;
                  },
                  'for' => sub {
                     my $found = 0;
                     for my $iter (10_000..10_100) { # 101 searches
                        foreach (@a) {
                           $found = 1 and last if $iter == $_;
                        }
                     }
                     return $found;
                  },
                 });
[download]

This gives the results:

Benchmark: timing 20 iterations of for, hash...
       for: 16 wallclock secs (15.67 usr +  0.00 sys = 15.67 CPU) @  1
+.28/s (n=20)
      hash:  8 wallclock secs ( 8.57 usr +  0.04 sys =  8.61 CPU) @  2
+.32/s (n=20)
       Rate  for hash
for  1.28/s   -- -45%
hash 2.32/s  82%   --
[download]

So hashes are faster for 101 searches of the same 100_000 element array; crossover is at about 70 searches on my machine.

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