use strict;
use warnings;
use Benchmark;
use List::Util qw /shuffle/;
use feature 'say';
my $n = 10**7;
my @sorted = 1..$n;
my @random =  shuffle @sorted;

my $t0 = Benchmark->new;
    say sum_this(\@sorted);
    my $t1 = Benchmark->new;
    my $td1 = timediff($t1, $t0);
    say "sorted:",timestr($td1);
    my $t2 = Benchmark->new;
    say sum_this(\@random);
    my $t3 = Benchmark->new;
    my $td2 = timediff($t3, $t2);
    say "random:",timestr($td2);



sub sum_this {
        my ($arr) = @_;
        my $sum;
        foreach (my $i=0;$i<=$#$arr;$i++) {
        my $x = $arr->[$i];
        if($x>$n/2) {
                $sum+= $x;
        }

}
return $sum;
}
[download]

37500002500000
sorted: 6 wallclock secs ( 5.61 usr +  0.00 sys =  5.61 CPU)
37500002500000
random: 6 wallclock secs ( 5.81 usr +  0.00 sys =  5.81 CPU)