Perl implement Tree data structure (2)

之前用struct实现的Tree不够灵活，重新使用hash来实现，更加灵活而且可以更改节点，进而实现平衡二叉树。

以下为程序代码：

use Data::Dumper;

my $tree = {};

add($tree,$_) for (5,7,1,4,9,6,100,20,30,21,60);
print Dumper $tree;
LMR($tree,$tree->{root});
rml($tree,$tree->{root});

sub add{
    my ($tree,$value) = @_;
    return if exists $tree->{$value};
    
    if (! exists $tree->{root}){
        $tree->{$value} = undef;
        $tree->{root} = $value;
        return
    }
    
    my $tmp = $tree->{root};
    while(defined $tmp){
        if ($value < $tmp){
            if (exists $tree->{$tmp}->{left}){
                $tmp = $tree->{$tmp}->{left}
            }
            else{
                $tree->{$value} = undef;
                $tree->{$tmp}->{left} = $value;
                return
            }
        }
        elsif($value > $tmp){
            if (exists $tree->{$tmp}->{right}){
                $tmp = $tree->{$tmp}->{right}
            }
            else{
                $tree->{$value} = undef;
                $tree->{$tmp}->{right} = $value;
                return
            }
        }
    }
}

sub LMR{
    my ($tree,$root) = @_;
    
    if (exists $tree->{$root}->{left}){
        LMR($tree,$tree->{$root}->{left})
    }
    print "$root ";
    if (exists $tree->{$root}->{right}){
        LMR($tree,$tree->{$root}->{right})
    }        
}

sub rml{
    my ($tree,$root) = @_;
    
    if (exists $tree->{$root}->{right}){
        rml($tree,$tree->{$root}->{right})
    }
    print "$root ";
    if (exists $tree->{$root}->{left}){
        rml($tree,$tree->{$root}->{left})
    }

}