Just to be thorough, I thought I'd include some testing code to give more hints as to how this is supposed to work.

#!/usr/bin/perl

use warnings;
use strict;

use Data::Dumper;

# Be sure to copy the subroutine code into here.


my @tree1 = (
              [
                [ 'red',    'orange',  'yellow',   undef,      undef, 
+    undef   ],
                [ undef,    undef,     undef,      'cyan',     'magent
+a', 'black' ]
              ],
              [
                [ 'red',    undef,     'yellow',   undef,      'magent
+a', undef   ],
                [ undef,    'orange',  undef,      'cyan',     undef, 
+    'black' ]
              ],    );


my @done =(
            [
              [ 'red',      'orange',  'yellow',   'cyan',     'magent
+a', 'black' ],
              [ 'red',      'orange',  'yellow',   'cyan',     'magent
+a', 'black' ]
            ]
          );

my @tree2 = Combine_Branches (\@tree1, 1, 3);

my $done_string   = Dumper(@done);
my $tree2_string  = Dumper(@tree2);

print "Combine_Branches(\@tree1, 0, 3);\n";
if ( $done_string ne $tree2_string ) {
  print "Ack, not the same.\n";
  print "$tree2_string\n";
  print "$done_string\n";
} else {
  print "Everything is joy.\n"
}
[download]

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