Merge pull request #107 from kirilcvetkov/SinglyLinkedLists

Added Singly Linked Lists

Author: darwinz

DataStructures/SinglyLinkedList.php

@@ -0,0 +1,47 @@
+<?php
+/**
+ *  Singly Linked List
+ */
+
+class SinglyLinkedList
+{
+    public ?SinglyLinkedList $next = null;
+    public $data;
+
+    public function __construct($data)
+    {
+        $this->data = $data;
+    }
+
+    public function append($data): void
+    {
+        $current = $this;
+
+        while ($current instanceof SinglyLinkedList && isset($current->next)) {
+            $current = $current->next;
+        }
+
+        $current->next = new SinglyLinkedList($data);
+    }
+
+    public function delete($data): SinglyLinkedList
+    {
+        $current = $this;
+
+        if ($current->data == $data) {
+            return $current->next;
+        }
+
+        while ($current instanceof SinglyLinkedList && isset($current->next)) {
+            if ($current->next->data === $data) {
+                $current->next = $current->next->next;
+
+                return $this;
+            }
+
+            $current = $current->next;
+        }
+
+        return $this;
+    }
+}

tests/DataStructures/SinglyLinkedListTest.php

@@ -0,0 +1,135 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+require_once __DIR__ . '/../../DataStructures/SinglyLinkedList.php';
+
+/**
+ * Tests for the Singly Linked Lists class
+ */
+class SinglyLinkedListTest extends TestCase
+{
+    /**
+     * Create a SinglyLinkedList node
+     */
+    private function createNode(string $string): SinglyLinkedList
+    {
+        $node = new SinglyLinkedList($string[0]);
+
+        for ($i = 1; $i < strlen($string); $i++) {
+            $node->append($string[$i]);
+        }
+
+        return $node;
+    }
+
+    /**
+     * Provider of SinglyLinkedList nodes
+     */
+    public function provideNodes()
+    {
+        return [
+            'IsPalindrome' => [
+                'node' => $this->createNode('hannah'),
+                'expected' => true
+            ],
+            'IsPalindrome2' => [
+                'node' => $this->createNode('hanah'),
+                'expected' => true
+            ],
+            'IsNotPalindrome' => [
+                'node' => $this->createNode('hanbah'),
+                'expected' => false
+            ],
+            'IsNotPalindrome2' => [
+                'node' => $this->createNode('han1h'),
+                'expected' => false
+            ],
+        ];
+    }
+
+    /**
+     * Test the if a SinglyLinkedList is a palindrome
+     *
+     * @dataProvider provideNodes
+     */
+    public function testIsPalindrome($node, $expected): void
+    {
+        $this->assertEquals($expected, $this->isPalindrome($node));
+    }
+
+    /**
+     * Supporting method for testing if a linked list is palindrome
+     */
+    private function isPalindrome(SinglyLinkedList $node): bool
+    {
+        $length = $this->length($node);
+        $pairs = 0;
+        $curr = $node;
+
+        while ($curr instanceof SinglyLinkedList) {
+            if ($this->hasPair($curr->next, $curr->data)) {
+                $pairs++;
+            }
+
+            $curr = $curr->next;
+        }
+
+        return $pairs == floor($length / 2);
+    }
+
+    /**
+     * Supporting method for testing if a linked list is palindrome
+     */
+    private function hasPair($node, string $data): bool
+    {
+        if (! $node instanceof SinglyLinkedList) {
+            return false;
+        }
+
+        $curr = $node;
+
+        while ($curr instanceof SinglyLinkedList) {
+            if ($curr->data == $data) {
+                return true;
+            }
+
+            $curr = $curr->next;
+        }
+
+        return false;
+    }
+
+    /**
+     * Supporting method for testing if a linked list is palindrome
+     */
+    private function length(SinglyLinkedList $node): int
+    {
+        $curr = $node;
+        $counter = 0;
+
+        while ($curr instanceof SinglyLinkedList) {
+            $counter++;
+            $curr = $curr->next;
+        }
+
+        return $counter;
+    }
+
+    /**
+     * Test SinglyLinkedList's delete functionality
+     */
+    public function testDelete(): void
+    {
+        $this->assertEquals(
+            $this->createNode('hanah'), // expected node
+            $this->createNode('hannah')->delete('n'), // actual node
+        );
+
+        $this->assertNotEquals(
+            $this->createNode('hanah'), // expected node
+            $this->createNode('hannah')->delete('h'), // actual node
+        );
+    }
+}