#!/usr/bin/env perl

my @arr=(); # ref to node, 0: head, 1: node1 addr, 2:node2 addr ...

# initialize 7 independent nodes
my $index=1;
foreach ('a' .. 'g') {
 $arr[$index]=[$_, undef]; # save anonymous array reference into @arr
 $index++;
}

my $head=['head', undef]; $arr[0]=$head;

# link these node together from head ->node1 ->node2 ->node3 .. node7->///
foreach (0 .. @arr){
 $arr[$_]->[1]= $arr[$_+1]; #form the link list
}

my $cur = $head; #current

#traverse
while ($cur->[1]){
 my $data = $cur->[0];
 print "$data ";
 $cur = $cur->[1];
}
print "$cur->[0]\n"; #last one


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

my @arr=(); # ref to node, 0: head, 1: node1 addr, 2:node2 addr ...

# initialize 7 independent nodes
my $index=1;
foreach ('a' .. 'g') {
 $arr[$index]=[$_, undef]; # save anonymous array reference into @arr
 $index++;
}

my $head=['head', undef]; $arr[@arr]=$head;

# link these node together from head ->node7 ->node6 ->node5 .. node1->///
foreach (0 .. @arr){
 my $index = @arr - $_;
 $arr[$index]->[1]= $arr[$index-1]; #form the link list
}

my $cur = $head; #current

#traverse
while ($cur->[1]){
 my $data = $cur->[0];
 print "$data ";
 $cur = $cur->[1];
}
print "$cur->[0]\n"; #last one


############333333333333333333
#!/usr/bin/env perl

my @arr=(); # ref to node, 0: head, 1: node1 addr, 2:node2 addr ...

# initialize 7 independent nodes
my $head=['head', undef]; $arr[0]=$head;

my $index=1;
foreach ('a' .. 'z') {
 $arr[$index]=[$_, undef]; # save anonymous array reference into @arr
 $index++;
}

# link these node together from head ->node1 ->node2 ->node3 .. node7->///
foreach (0 .. @arr){
 $arr[$_]->[1]= $arr[$_+1]; #form the link list
}

my $found=0;

print "input target: ";
chomp(my $target=<>);

my $cur=$head;
my $node_num=0;

#traverse
while ($cur->[1]){
 if ($cur->[0] eq $target) {
  $found=1;
  last;
 }
 $cur = $cur->[1];
 $node_num++;
}

if ($found){
 print "found and it is node$node_num\n";
}


###### page 107
#!/usr/bin/env perl

my %hash1 =('Jack', 'Chue', 'Danel', 'Eng');

my %hash2 = (
 'foo'  => 35,
 'bar'  => 12.4,
 2.5    => 'hello');


my %hash3 = (
 foo    => 35,
 bar    => 12.4,
 2.5    => 'hello');

foreach (keys %hash3){
 print "$_ $hash3{$_}\n";
}