Implemented Trie DataStructure

DataStructures/Trie/Trie.php

@@ -0,0 +1,163 @@
+<?php
+
+namespace DataStructures\Trie;
+
+class Trie
+{
+    private TrieNode $root;
+
+    public function __construct()
+    {
+        $this->root = new TrieNode();
+    }
+
+    /**
+     * Get the root node of the Trie.
+     */
+    public function getRoot(): TrieNode
+    {
+        return $this->root;
+    }
+
+    /**
+     * Insert a word into the Trie.
+     */
+    public function insert(string $word): void
+    {
+        $node = $this->root;
+        for ($i = 0; $i < strlen($word); $i++) {
+            $char = $word[$i];
+            $node = $node->addChild($char);
+        }
+        $node->isEndOfWord = true;
+    }
+
+    /**
+     * Search for a word in the Trie.
+     */
+    public function search(string $word): bool
+    {
+        $node = $this->root;
+        for ($i = 0; $i < strlen($word); $i++) {
+            $char = $word[$i];
+            if (!$node->hasChild($char)) {
+                return false;
+            }
+            $node = $node->getChild($char);
+        }
+        return $node->isEndOfWord;
+    }
+
+    /**
+     * Find all words that start with a given prefix.
+     */
+    public function startsWith(string $prefix): array
+    {
+        $node = $this->root;
+        for ($i = 0; $i < strlen($prefix); $i++) {
+            $char = $prefix[$i];
+            if (!$node->hasChild($char)) {
+                return [];
+            }
+            $node = $node->getChild($char);
+        }
+        return $this->findWordsFromNode($node, $prefix);
+    }
+
+    /**
+     * Helper function to find all words from a given node.
+     */
+    private function findWordsFromNode(TrieNode $node, string $prefix): array
+    {
+        $words = [];
+        if ($node->isEndOfWord) {
+            $words[] = $prefix;
+        }
+
+        foreach ($node->children as $char => $childNode) {
+            $words = array_merge($words, $this->findWordsFromNode($childNode, $prefix . $char));
+        }
+
+        return $words;
+    }
+
+    /**
+     * Delete a word from the Trie.
+     * Recursively traverses the Trie and removes nodes
+     *
+     * @param string $word The word to delete.
+     * @return bool Returns true if the word was successfully deleted, otherwise false.
+     */
+    public function delete(string $word): bool
+    {
+        return $this->deleteHelper($this->root, $word, 0);
+    }
+
+    /**
+     * Helper function for deleting a word.
+     * Recursively traverse the Trie and removes nodes.
+     *
+     * @param TrieNode $node The current node in the Trie.
+     * @param string $word The word being deleted.
+     * @param int $index The current index in the word.
+     * @return bool Returns true if the current node should be deleted, otherwise false.
+     */
+    private function deleteHelper(TrieNode $node, string &$word, int $index): bool
+    {
+        if ($index === strlen($word)) {
+            if (!$node->isEndOfWord) {
+                return false;
+            }
+            $node->isEndOfWord = false;
+            return empty($node->children);
+        }
+
+        $char = $word[$index];
+        $childNode = $node->getChild($char);
+        if ($childNode === null) {
+            return false;
+        }
+
+        // Recursively delete the child node
+        $shouldDeleteCurrentNode = $this->deleteHelper($childNode, $word, $index + 1);
+
+        if ($shouldDeleteCurrentNode) {
+            unset($node->children[$char]);
+            return !$node->isEndOfWord;     // true if current node is not the end of another word
+        }
+
+        return false;
+    }
+
+    /**
+     * Recursively traverses the Trie starting from the given node and collects all words.
+     *
+     * @param TrieNode $node The starting node for traversal.
+     * @param string $prefix The prefix of the current path in the Trie.
+     * @return array An array of words found in the Trie starting from the given node.
+     */
+    public function traverseTrieNode(TrieNode $node, string $prefix = ''): array
+    {
+        $words = [];
+
+        if ($node->isEndOfWord) {
+            $words[] = $prefix;
+        }
+
+        foreach ($node->children as $char => $childNode) {
+            $words = array_merge($words, $this->traverseTrieNode($childNode, $prefix . $char));
+        }
+
+        return $words;
+    }
+
+    /**
+     * Gets all words stored in the Trie.
+     *
+     * @return array An array of all words in the Trie.
+     */
+    public function getWords(): array
+    {
+        return $this->traverseTrieNode($this->root);
+    }
+}

DataStructures/Trie/TrieNode.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace DataStructures\Trie;
+
+class TrieNode
+{
+    /** @var array<string, TrieNode> */
+    public array $children;
+    public bool $isEndOfWord;
+
+    public function __construct()
+    {
+        $this->children = [];  // Associative array where [ char => TrieNode ]
+        $this->isEndOfWord = false;
+    }
+
+    /**
+     * Add a child node for a character.
+     */
+    public function addChild(string $char): TrieNode
+    {
+        if (!isset($this->children[$char])) {
+            $this->children[$char] = new TrieNode();
+        }
+        return $this->children[$char];
+    }
+
+    /**
+     * Check if a character has a child node.
+     */
+    public function hasChild(string $char): bool
+    {
+        return isset($this->children[$char]);
+    }
+
+    /**
+     * Get the child node corresponding to a character.
+     */
+    public function getChild(string $char): ?TrieNode
+    {
+        return $this->children[$char] ?? null;
+    }
+}

tests/DataStructures/TrieTest.php

@@ -0,0 +1,137 @@
+<?php
+
+namespace DataStructures;
+
+require_once __DIR__ . '/../../DataStructures/Trie/Trie.php';
+require_once __DIR__ . '/../../DataStructures/Trie/TrieNode.php';
+
+use DataStructures\Trie\Trie;
+use PHPUnit\Framework\TestCase;
+
+class TrieTest extends TestCase
+{
+    private Trie $trie;
+
+    protected function setUp(): void
+    {
+        $this->trie = new Trie();
+    }
+
+    public function testInsertAndSearch()
+    {
+        $this->trie->insert('the');
+        $this->trie->insert('universe');
+        $this->trie->insert('is');
+        $this->trie->insert('vast');
+
+        $this->assertTrue($this->trie->search('the'), 'Expected "the" to be found in the Trie.');
+        $this->assertTrue($this->trie->search('universe'), 'Expected "universe" to be found in the Trie.');
+        $this->assertTrue($this->trie->search('is'), 'Expected "is" to be found in the Trie.');
+        $this->assertTrue($this->trie->search('vast'), 'Expected "vast" to be found in the Trie.');
+        $this->assertFalse(
+            $this->trie->search('the universe'),
+            'Expected "the universe" not to be found in the Trie.'
+        );
+    }
+
+    public function testStartsWith()
+    {
+        $this->trie->insert('hello');
+        $this->assertEquals(['hello'], $this->trie->startsWith('he'), 'Expected words starting with "he" to be found.');
+        $this->assertEquals(
+            ['hello'],
+            $this->trie->startsWith('hello'),
+            'Expected words starting with "hello" to be found.'
+        );
+        $this->assertEquals(
+            [],
+            $this->trie->startsWith('world'),
+            'Expected no words starting with "world" to be found.'
+        );
+    }
+
+    public function testDelete()
+    {
+        // Insert words into the Trie
+        $this->trie->insert('the');
+        $this->trie->insert('universe');
+        $this->trie->insert('is');
+        $this->trie->insert('vast');
+        $this->trie->insert('big');
+        $this->trie->insert('rather');
+
+        // Test deleting an existing word
+        $this->trie->delete('the');
+        $this->assertFalse($this->trie->search('the'), 'Expected "the" not to be found after deletion.');
+
+        // Test that other words are still present
+        $this->assertTrue($this->trie->search('universe'), 'Expected "universe" to be found.');
+        $this->assertTrue($this->trie->search('is'), 'Expected "is" to be found.');
+        $this->assertTrue($this->trie->search('vast'), 'Expected "vast" to be found.');
+        $this->assertTrue($this->trie->search('big'), 'Expected "big" to be found.');
+        $this->assertTrue($this->trie->search('rather'), 'Expected "rather" to be found.');
+    }
+
+    public function testDeleteNonExistentWord()
+    {
+        $this->trie->delete('nonexistent');
+        $this->assertFalse($this->trie->search('nonexistent'), 'Expected "nonexistent" to not be found.');
+    }
+
+    public function testTraverseTrieNode()
+    {
+        $this->trie->insert('hello');
+        $this->trie->insert('helium');
+        $this->trie->insert('helicopter');
+
+        $words = $this->trie->getWords();
+        $this->assertContains('hello', $words, 'Expected "hello" to be found in the Trie.');
+        $this->assertContains('helium', $words, 'Expected "helium" to be found in the Trie.');
+        $this->assertContains('helicopter', $words, 'Expected "helicopter" to be found in the Trie.');
+        $this->assertCount(3, $words, 'Expected 3 words in the Trie.');
+    }
+
+    public function testEmptyTrie()
+    {
+        $this->assertEquals([], $this->trie->getWords(), 'Expected an empty Trie to return an empty array.');
+    }
+
+    public function testGetWords()
+    {
+        $this->trie->insert('apple');
+        $this->trie->insert('app');
+        $this->trie->insert('applet');
+
+        $words = $this->trie->getWords();
+        $this->assertContains('apple', $words, 'Expected "apple" to be found in the Trie.');
+        $this->assertContains('app', $words, 'Expected "app" to be found in the Trie.');
+        $this->assertContains('applet', $words, 'Expected "applet" to be found in the Trie.');
+        $this->assertCount(3, $words, 'Expected 3 words in the Trie.');
+    }
+
+    public function testInsertEmptyString()
+    {
+        $this->trie->insert('');
+        $this->assertTrue($this->trie->search(''), 'Expected empty string to be found in the Trie.');
+    }
+
+    public function testDeleteEmptyString()
+    {
+        $this->trie->insert('');
+        $this->trie->delete('');
+        $this->assertFalse($this->trie->search(''), 'Expected empty string not to be found after deletion.');
+    }
+
+    public function testStartsWithWithCommonPrefix()
+    {
+        $this->trie->insert('trie');
+        $this->trie->insert('tried');
+        $this->trie->insert('trier');
+
+        $words = $this->trie->startsWith('tri');
+        $this->assertContains('trie', $words, 'Expected "trie" to be found with prefix "tri".');
+        $this->assertContains('tried', $words, 'Expected "tried" to be found with prefix "tri".');
+        $this->assertContains('trier', $words, 'Expected "trier" to be found with prefix "tri".');
+        $this->assertCount(3, $words, 'Expected 3 words with prefix "tri".');
+    }
+}