use Data::Dump 'dd';
use strict;
use warnings;

dd my $h1 = { a => {b => {c => 1}, d=> 2}, e=>3,f=>4 };
dd my $h2 = { a => {b => {c => 1}, d=> 2}, e=>3,f=>4 };

sub gen {
  my $ref=shift;
  my @path=();
  return sub {
    while (1) {
      while (my ($k,$v) = each %$ref) {
        if ( ref $v eq "HASH") {
          push @path,$ref;
          $ref =$v;
          next;
        } else {
          return $k,$v,scalar @path;
        }
      }
      return unless  $ref = pop @path;
    }
  }
}

my $iter1=gen($h1);
my $iter2=gen($h2);

while ((my ($k1,$v1,$l1) = $iter1->()) + (my ($k2,$v2,$l2) = $iter2->()) ) {
  die "error $v1 != $v2" if $v1 ne $v2; 
  print "$l1: $k1=> $v1\n";
}