#!/usr/bin/perl

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

srand 0;
our %hash = map { rand() } 1..1000;

my $regular = sub {
    sort { $hash{$a} <=> $hash{$b} } keys %hash;
};

my $keysonly = sub {
    sort { $a <=> $b } keys %hash;
};

my $reverse_noref = sub {
    my %reverse_hash = ();
    foreach my $key (keys %hash) {
        $reverse_hash{$hash{$key}} = $key;
    }
    sort { $a <=> $b } keys %reverse_hash;
};

my $reverse = sub {
    my %reverse_hash = ();
    foreach my $key (keys %hash) {
        push @{ $reverse_hash{$hash{$key}} }, $key;
    }
    sort { $a <=> $b } keys %reverse_hash;
};

cmpthese(-2, {
    regular       => $regular,
    keysonly      => $keysonly,
    reverse       => $reverse,
    reverse_noref => $reverse_noref
});