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 PHP 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.php
Replay: real traced execution (multi-file project)
<?php
class Node {
    public int $value;
    public ?Node $next;
    public function __construct(int $value, ?Node $next = null) {
        $this->value = $value;
        $this->next = $next;
    }
}
function render_chain(?Node $head): string {
    $parts = [];
    $cursor = $head;
    while ($cursor !== null) {
        $parts[] = (string)$cursor->value;
        $cursor = $cursor->next;
    }
    return implode(" -> ", $parts) . " -> null";
}
$head = new Node(10, new Node(20, new Node(30)));
echo render_chain($head) . PHP_EOL;

  1. head ← 10 -> 20 -> 30 -> null

    1<?php2class Node {
    values this step10 -> 20 -> 30 -> nullhead

  2. output ← 10

    12$cursor = $head;13while ($cursor !== null) {14    $parts[] = (string)$cursor->value;
    values this step10outputnode(10)cursor

  3. output ← 10 -> 20

    12$cursor = $head;13while ($cursor !== null) {14    $parts[] = (string)$cursor->value;
    values this step10 -> 20outputnode(20)cursor

  4. output ← 10 -> 20 -> 30 -> null

    12$cursor = $head;13while ($cursor !== null) {14    $parts[] = (string)$cursor->value;
    values this step10 -> 20 -> 30 -> nulloutputnode(30)cursor

  5. stdout ← 10 -> 20 -> 30 -> null

    19$head = new Node(10, new Node(20, new Node(30)));20echo render_chain($head) . PHP_EOL;
    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.