Linked Structures

Traverse and Print

Walk from the head pointer to null, visiting each node exactly once without random indexing.

Algorithm

The replay labels nodes by value, such as node(20), and never exposes object identity or memory addresses. This Perl DSA implementation uses the same small chain as the rest of the DSA track.

cursor A cursor reference names the node currently being visited.
null stop Traversal ends when the cursor reaches the null marker.

Basic Implementation

basic.pl
Replay: real traced execution (multi-file project)
use strict;
use warnings;

sub node {
    my ($value, $next) = @_;
    return { value => $value, next => $next };
}

sub render {
    my ($head) = @_;
    my @parts;
    my $cursor = $head;
    while (defined $cursor) {
        push @parts, $cursor->{value};
        $cursor = $cursor->{next};
    }
    return join(" -> ", @parts) . " -> null";
}

my $head = node(10, node(20, node(30, undef)));
print render($head), "\n";

  1. head ← 10 -> 20 -> 30 -> null

    1use strict;2use warnings;
    values this step10 -> 20 -> 30 -> nullhead

  2. output ← 10

    12my $cursor = $head;13while (defined $cursor) {14    push @parts, $cursor->{value};
    values this step10outputnode(10)cursor

  3. output ← 10 -> 20

    12my $cursor = $head;13while (defined $cursor) {14    push @parts, $cursor->{value};
    values this step10 -> 20outputnode(20)cursor

  4. output ← 10 -> 20 -> 30 -> null

    12my $cursor = $head;13while (defined $cursor) {14    push @parts, $cursor->{value};
    values this step10 -> 20 -> 30 -> nulloutputnode(30)cursor

  5. stdout ← 10 -> 20 -> 30 -> null

    20my $head = node(10, node(20, node(30, undef)));21print render($head), "\n";
    values this step10 -> 20 -> 30 -> nullstdout10 -> 20 -> 30 -> nulloutput

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation notes

  • Keep the explicit node and pointer/reference operations; array shortcuts hide the linked-list state this lesson is meant to replay.
  • The final output prints the chain in a deterministic a -> b -> null form for cross-language comparison.