Kind of an odd question, they are not the same key value pairs; unless you mean numeral versus spelled number(?). They are flipped key value pairs. You have to make a choice which is the side to remove or call a duplicate. This may or may not do what you expect–

use Data::Dump "pp";
my %hash = ('one' => '1', 'two' => '2','1'=>'one');
my %seen;
for my $key ( keys %hash )
{
    delete $hash{$key} if $seen{$key} || $seen{$hash{$key}};
    $seen{$key}++;
    $seen{$hash{$key}}++;
}
pp \%hash;
--
{ 1 => "one", two => 2 }
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