for ($i = 0; $i < 50; $i++) { #loop over array of hashes (each subset will have 50 keys)
    foreach my $key (keys $subsets[$i]) { #5 keys at each level
        my $max = 0;
        my @max;
        for my $key1 (keys %distances) {
            if $key !exists (keys %used) {
                $max = max (values %{$distances{$key1}});
                push @max, $max;
                # somehow retrieve the 2nd key
            }
        }
        my $maxmax = max @max;
        # $subsets[$i+1]{2nd_key_with_max_val} = "e.g. C1"
        # push %used with key and value
        @max = [];
    }
}