Linked Structures

Delete by Value

Find the node before the target value and rewire its next pointer so the target node leaves the chain.

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.

predecessor Deletion needs the node before the one being removed.
rewiring The predecessor skips the target and points at the target's next node.

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, new Node(40))));
$target = 30;
$cursor = $head;
while ($cursor->next !== null) {
    if ($cursor->next->value === $target) {
        $cursor->next = $cursor->next->next;
        break;
    }
    $cursor = $cursor->next;
}
echo render_chain($head) . PHP_EOL;

  1. head ← 10 -> 20 -> 30 -> 40 -> null, target ← 30

    1<?php2class Node {
    values this step10 -> 20 -> 30 -> 40 -> nullhead30target

  2. cursor ← node(20)

    12$cursor = $head;13while ($cursor !== null) {14    $parts[] = (string)$cursor->value;
    values this stepnode(10) → node(20)cursor

  3. cursor.next ← node(40)

    1<?php2class Node {
    values this stepnode(30) → node(40)cursor.next

  4. stdout ← 10 -> 20 -> 40 -> null

    28}29echo render_chain($head) . PHP_EOL;
    values this step10 -> 20 -> 40 -> nullstdout10 -> 20 -> 40 -> nullhead

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.