Add LinkedList Implementation and Comprehensive Unit Tests

src/Collection/LinkedList.php

@@ -0,0 +1,154 @@
+<?php
+
+declare(strict_types=1);
+
+namespace KaririCode\DataStructure\Collection;
+
+use KaririCode\Contract\DataStructure\Structural\Collection;
+use KaririCode\DataStructure\Node;
+
+/**
+ * LinkedList implementation.
+ *
+ * This class implements a doubly-linked list, providing O(1) time complexity
+ * for adding and removing elements at both ends, and O(n) for arbitrary index access.
+ *
+ * @category  Collections
+ *
+ * @author    Walmir Silva <walmir.silva@kariricode.org>
+ * @license   MIT
+ *
+ * @see       https://kariricode.org/
+ */
+class LinkedList implements Collection
+{
+    private ?Node $head = null;
+    private ?Node $tail = null;
+    private int $size = 0;
+
+    public function add(mixed $element): void
+    {
+        $newNode = new Node($element, $this->tail);
+        if ($this->tail) {
+            $this->tail->next = $newNode;
+        } else {
+            $this->head = $newNode;
+        }
+        $this->tail = $newNode;
+        ++$this->size;
+    }
+
+    public function addAll(Collection $collection): void
+    {
+        foreach ($collection->getItems() as $element) {
+            $this->add($element);
+        }
+    }
+
+    public function remove(mixed $element): bool
+    {
+        $current = $this->head;
+        while (null !== $current) {
+            if ($current->data === $element) {
+                if ($current->prev) {
+                    $current->prev->next = $current->next;
+                } else {
+                    $this->head = $current->next;
+                }
+                if ($current->next) {
+                    $current->next->prev = $current->prev;
+                } else {
+                    $this->tail = $current->prev;
+                }
+                --$this->size;
+
+                return true;
+            }
+            $current = $current->next;
+        }
+
+        return false;
+    }
+
+    public function contains(mixed $element): bool
+    {
+        $current = $this->head;
+        while (null !== $current) {
+            if ($current->data === $element) {
+                return true;
+            }
+            $current = $current->next;
+        }
+
+        return false;
+    }
+
+    public function clear(): void
+    {
+        $this->head = null;
+        $this->tail = null;
+        $this->size = 0;
+    }
+
+    public function isEmpty(): bool
+    {
+        return 0 === $this->size;
+    }
+
+    public function getItems(): array
+    {
+        $items = [];
+        $current = $this->head;
+        while (null !== $current) {
+            $items[] = $current->data;
+            $current = $current->next;
+        }
+
+        return $items;
+    }
+
+    public function count(): int
+    {
+        return $this->size;
+    }
+
+    public function get(int $index): mixed
+    {
+        if ($index < 0 || $index >= $this->size) {
+            throw new \OutOfRangeException("Index out of range: $index");
+        }
+        $current = $this->head;
+        for ($i = 0; $i < $index; ++$i) {
+            $current = $current->next;
+        }
+
+        return $current->data;
+    }
+
+    public function set(int $index, mixed $element): void
+    {
+        if ($index < 0 || $index >= $this->size) {
+            throw new \OutOfRangeException("Index out of range: $index");
+        }
+        $current = $this->head;
+        for ($i = 0; $i < $index; ++$i) {
+            $current = $current->next;
+        }
+        $current->data = $element;
+    }
+
+    /**
+    * Clone method to ensure deep copy of nodes
+    */
+    public function __clone()
+    {
+        $newList = new LinkedList();
+        $current = $this->head;
+        while ($current !== null) {
+            $newList->add($current->data);
+            $current = $current->next;
+        }
+        $this->head = $newList->head;
+        $this->tail = $newList->tail;
+    }
+}

src/Node.php

@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace KaririCode\DataStructure;
+
+class Node
+{
+    public function __construct(
+        public mixed $data,
+        public ?Node $prev = null,
+        public ?Node $next = null
+    ) {
+    }
+}