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my %hash = (
    'key1' => [1, 20, 3],
...
while(my ($k, $v) = each %hash) {
    push @{$rev_hash{$_}}, $k for @$v;
}

$_ = join ' ', sort @$_  for values %rev_hash;

...
while(my ($k, $v) = each %rev_hash) {
    push @{$inv_hash{$v}}, $k;
}

$_ = join ' ', sort {$a<=>$b} @$_  for values %inv_hash;

my %revinv_hash = reverse %inv_hash;