Okay this version finds the ends of the paths, then builds them backwards from their. As long as the data is good it will run fine ;) I added the pair (1,2) which breaks the above code.
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my $pairs = {
(4,-1),
(2,6),
(6,4),
(1,2),
(3,5),
(5,-1),
(99,-1),
};
my @paths;
#get the ends of all the chains
#then the next pieces, and so on, until all pairs are used.
for my $key ( grep { $pairs->{$_} == -1 } keys %$pairs ) {
push @paths, [$key, -1];
delete $pairs->{$key};
}
while ( keys %$pairs ) {
for my $path ( @paths ) {
for my $key ( keys %$pairs ) {
if ($pairs->{$key} eq @$path[0]) {
unshift @$path, $key;
delete $pairs->{$key};
}
}
}
}
my $hh;
for my $path (@paths) {
my $temp = pop @$path;
my $key = shift @$path;
for (reverse @$path) {
my $t = {$_ => $temp};
$temp = $t;
}
$hh->{$key} = $temp;
}
print Dumper($hh);
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