Here's a version of the same algorithm working on array elements instead of characters. (Messier, isn't it?)
With 10 elements (states) it takes 1.5 seconds on my machine, but I think most of the time is taken by the printing.
How many neighbors can you have? (for code testing purposes.)
#!/usr/bin/perl -l
# http://perlmonks.org/?node_id=1198509
use strict;
use warnings;
my @elements = (0, 2, 3);
@elements = 0..9;
my ($first, $last) = @elements[0, -1];
my %next;
@next{@elements} = @elements[1 .. $#elements];
for my $count (1,2,3,4,7,8)
{
print "count=$count";
my @set = ($first) x $count;
local $, = ',';
while(1)
{
print @set;
my $i = $#set;
$i-- while $i >= 0 and $set[$i] eq $last;
$i < 0 and last;
@set[$i .. $#set] = ($next{$set[$i]}) x ( @set - $i);
}
}
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