#!/usr/bin/env perl

#my @tree = (0,['+',2,3],['A'],['B']); # A+B
my @tree = (0,['+',2,3],['*',4,5],['B'], ['C'], ['D']);

sub post_order {
 my $nodeN = shift;
 return unless $tree[$nodeN][0];

 post_order($nodeN*2  );
 post_order($nodeN*2+1);
 print $tree[$nodeN][0];
}

sub in_order {
 my $nodeN = shift;
 return unless $tree[$nodeN][0];

 in_order($nodeN*2  );
 print $tree[$nodeN][0];
 in_order($nodeN*2+1);
}

post_order(1); print "\n";
in_order(1); print "\n";

#####
#!/usr/bin/env perl

my @tree = (    0,              #useless
                ['+',2,3],      #1 node1 data='+' left is node2, right is node3
                ['x'],          #2 node2 data='x' no left, no right
                ['*',6,7],      #3 node3 data='*' left is node4 right is node5
                [],             #4 nothing, no data, no left, no right, but occupy a space just do nothing
                [],             #5
                ['-',12,13],    #6
                ['w'],          #7
                [],             #8
                [],             #9
                [],             #10
                [],             #11
                ['y'],          #12
                ['z'],          #13
);


#### array ref
#!/usr/bin/env perl

#        +
#     X     Y
#

my $tree = [
            '+',[
                  'X',
                ],
                [ #2R
                  'Y',
                ],
          ];#tree

sub in_order {
 my $t = shift;
 return unless $t;

 in_order($$t[1]);
 print $$t[0];
 in_order($$t[2]);
}

sub post_order {
 my $t = shift;
 return unless $t;

 post_order($$t[1]);
 post_order($$t[2]);
 print $$t[0];
}

in_order($tree); print "\n";
post_order($tree); print "\n";