Here goes, interesting little problem ... my solution is non-recursive, can handle loops and allows to write
my @order = demangle(\%replace);.
Update
After sleeping over it I've greatly simplified the algoritm, now I think it's elegant. You have to decide yourself if this algorithm is nicer than the rather elegant recursive solution.
sub demangle {
my $r = shift;
my %illegal;
@illegal{%$r} = ();
my @chains;
LOOP:
while (my($k,$v) = each %$r) {
for my $c (@chains) {
if ($c->[-1] eq $k) { # append to end of chain
push @$c, $v;
next LOOP;
};
if ($c->[0] eq $v) { # prepend to start of chain
unshift @$c, $k;
next LOOP;
}
}
push @chains, [$k, $v]; # create new chain
}
# fix circular replacements
for my $c (@chains) {
if ($c->[0] eq $c->[-1]) { # we have a circle
my $new_key;
do {
$new_key = join '', map { ('a'..'z')[rand 26] } 1..8;
} while exists $illegal{$new_key};
$illegal{$new_key}++;
unshift @$c, $new_key;
push @$c, $new_key;
}
}
my @order;
while (@chains) {
push @order, { map { $_->[-2] => pop @$_ } @chains };
@chains = grep @$_ > 1, @chains;
}
return @order;
}
-- Hofmator