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

my %hash = (a => 1, b => 2, c => 3, d => 2, e => 5, f => 3);
my %HoA;
for my $key (keys %hash) {
	my $value = $hash{$key};
	push @{$HoA{$value}}, $key;
}
for my $key2 (keys %HoA) {
	my @keys = @{$HoA{$key2}};
	say "Keys @keys have the same value: $key2 ";
}