Add design-linked-list solution

Author: imajinyun

src/leetcode/DesignLinkedList.php

@@ -0,0 +1,125 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode;
+
+use leetcode\util\ListNode;
+
+class DesignLinkedList
+{
+    private int $size;
+
+    private ?ListNode $head;
+
+    /**
+     * Initialize your data structure here.
+     */
+    public function __construct()
+    {
+        $this->size = 0;
+        $this->head = null;
+    }
+
+    /**
+     * Get the value of the index-th node in the linked list.
+     * If the index is invalid, return -1.
+     *
+     * @param int $index
+     *
+     * @return int
+     */
+    public function get(int $index): int
+    {
+        if ($index < 0 || $index >= $this->size) {
+            return -1;
+        }
+        $curr = $this->head;
+        for ($i = 0; $i < $index; $i++) {
+            $curr = $curr->next;
+        }
+
+        return $curr->val;
+    }
+
+    /**
+     * Add a node of value val before the first element of the linked list.
+     * After the insertion, the new node will be the first node of the linked list.
+     *
+     * @param int $val
+     *
+     * @return null
+     */
+    public function addAtHead(int $val): void
+    {
+        $this->addAtIndex(0, $val);
+    }
+
+    /**
+     * Append a node of value val to the last element of the linked list.
+     *
+     * @param int $val
+     *
+     * @return null
+     */
+    public function addAtTail($val): void
+    {
+        $this->addAtIndex($this->size, $val);
+    }
+
+    /**
+     * Add a node of value val before the index-th node in the linked list.
+     * If index equals to the length of linked list,
+     * the node will be appended to the end of linked list.
+     * If index is greater than the length, the node will not be inserted.
+     *
+     * @param int $index
+     * @param int $val
+     *
+     * @return null
+     */
+    public function addAtIndex(int $index, int $val): void
+    {
+        if ($index > $this->size) {
+            return;
+        }
+        $node = new ListNode($val);
+        $curr = $this->head;
+
+        if ($index <= 0) {
+            $node->next = $curr;
+            $this->head = $node;
+        } else {
+            for ($i = 0; $i < $index - 1; $i++) {
+                $curr = $curr->next;
+            }
+            $node->next = $curr->next;
+            $curr->next = $node;
+        }
+        $this->size++;
+    }
+
+    /**
+     * Delete the index-th node in the linked list, if the index is valid.
+     *
+     * @param int $index
+     *
+     * @return null
+     */
+    public function deleteAtIndex(int $index): void
+    {
+        if ($index < 0 || $index >= $this->size) {
+            return;
+        }
+        $curr = $this->head;
+        if ($index === 0) {
+            $this->head = $curr->next;
+        } else {
+            for ($i = 0; $i < $index - 1; $i++) {
+                $curr = $curr->next;
+            }
+            $curr->next = $curr->next->next;
+        }
+        $this->size--;
+    }
+}

tests/leetcode/DesignLinkedListTest.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace leetcode\tests;
+
+use PHPUnit\Framework\TestCase;
+use leetcode\DesignLinkedList;
+
+class DesignLinkedListTest extends TestCase
+{
+    public function testDesignLinkedList(): void
+    {
+        $object = new DesignLinkedList();
+        self::assertSame(-1, $object->get(3));
+
+        $object->addAtHead(1);
+        self::assertSame(1, $object->get(0));
+
+        $object->addAtTail(3);
+        self::assertSame(3, $object->get(1));
+
+        $object->addAtIndex(1, 2);
+        self::assertSame(2, $object->get(1));
+
+        $object->deleteAtIndex(1);
+        self::assertSame(1, $object->get(0));
+        self::assertSame(3, $object->get(1));
+        self::assertSame(-1, $object->get(2));
+    }
+
+    public function testDesignLinkedList2(): void
+    {
+        $object = new DesignLinkedList();
+        $object->addAtHead(1);
+        self::assertSame(1, $object->get(0));
+
+        $object->addAtTail(3);
+        self::assertSame(3, $object->get(1));
+
+        $object->addAtIndex(1, 2);
+        self::assertSame(2, $object->get(1));
+
+        $object->deleteAtIndex(0);
+        self::assertSame(2, $object->get(0));
+    }
+}