in reply to How to get a ideal hash

Be well,
rir
#!/usr/bin/perl use strict; use warnings; use Data::Dumper; my $h = { 4 => -1, 2 => 6, 6 => 4, 3 => 5, 5 => -1, 99 => -1 }; sub LEAF() { -1 } # Make a list of toplevel keys: values occurring once and not LEAF my %tl; ++$tl{$_} for grep { $_ != LEAF } %$h ; my @toplevel = grep { $tl{$_} == 1 } keys %tl; # Build linked lists from head as HoHo... my %answer = (); for my $k ( @toplevel ) { my $cursor = \%answer; $cursor->{$k} = $h->{$k}; while ( LEAF != ( my $next_k = $cursor->{$k}) ) { $cursor = $cursor->{$k} = { $next_k, $h->{ $next_k } }; $k = $next_k; } } print Dumper \%answer;