Non-unique key in associative array

[csdude55]

I originally began with this:

###
$first = param('original');
$second = param('second');

%arr = (
'yellow' => 'blue',
'red' => 'green'
);

if ($arr{$first} eq $second || $arr{$second} eq $first) { $filter = 1; }
###

So if $first is "yellow" and $second is "blue", OR if $first is "blue" and $second is "yellow", then $filter will be set.

In practice, I have about 70 keys. But over time, I'm having to deal with duplicate possibilities. So in theory, I wrote this:

###
%arr = (
'yellow' => 'blue',
'yellow' => 'green',
'yellow' => 'red',

'red' => 'green'
);

if ($arr{$first} eq $second || $arr{$second} eq $first) { $filter = 1; }
###

But of course, this doesn't work because $arr{'yellow'} now equals "red", so "blue" or "green" would no longer match. And I can't just reverse it, because the values duplicate, too ("green" is a value for both "yellow" and "red").

I believe that I can fix it with a hash of arrays, so something like:

###
%arr = (
yellow => {
'blue' => 1,
'green' => 1,
'red' => 1
},

red => {
'green' => 1
}
);

if ($arr{$first}{$second} || $arr{$second}{$first}) { $filter = 1; }
###

Before I implement this, (1) do you guys see any problem with my coding, and (2) can you suggest a better / more readable way to do what I'm trying to do?

[csdude55]

Update... no, that doesn't quite work. The second part is the issue:

$arr{$second}{$first}

So if $first = 'red' and $second = 'green', it's not going to match.

I guess that I could make a second hash and invert all of the keys => values in a loop, but that seems like a pain and can't be the best option. Like this:

# Not tested, just typed for this post
%arr = ( 
 yellow => { 
  'blue' => 1, 
  'green' => 1, 
  'red' => 1 
 }, 

 red => { 
  'green' => 1 
 } 
); 

if ($arr{$first}{$second}) { $filter = 1; }

if (!$filter) {
 my %arr2;

 foreach $key (keys %arr) {
  foreach $key2 (keys %arr{$key}) {
   $arr2{$key2}{$key} = 1;
  }
 }

 if ($arr2{$first}{$second}) { $filter = 1; }
}

Any other suggestions?