chapter 8: dictionary and hash table

Author: loiane

src/06-linked-list/linked-list_.js

@@ -126,6 +126,16 @@ class LinkedList {
     return this.#size;
   }
 
+  forEach(callback) {
+    let current = this.#head;
+    let index = 0;
+    while (current) {
+      callback(current.data, index);
+      current = current.next;
+      index++;
+    }
+  }
+
   toString() {
     let current = this.#head;
     let objString = '';

src/08-dictionary-hash/01-using-dictionary-class.js

@@ -0,0 +1,42 @@
+// src/08-dictionary-hash/01-using-dictionary-class.js
+
+const Dictionary = require('./dictionary');
+
+const translations = new Dictionary();
+
+// Add some translations - English to Portuguese
+translations.set("hello", "olá"); 
+translations.set("thank you", "obrigado");
+translations.set("book", "livro");  
+translations.set("cat", "gato"); 
+translations.set("computer", "computador");
+
+// User interaction
+function translateWord(word) {
+  if (translations.hasKey(word)) {
+    const translation = translations.get(word);
+    console.log(`The translation of "${word}" is "${translation}"`);
+  } else {
+    console.log(`Sorry, no translation found for "${word}"`);
+  }
+}
+
+// Example usage
+translateWord("hello"); // Output: The translation of "hello" is "olá"
+translateWord("dog");  // Output: Sorry, no translation found for "dog"
+
+// Get all translations
+console.log("All translations:", translations.values());
+// All translations: [ 'olá', 'obrigado', 'livro', 'gato', 'computador' ]
+
+// Get all words
+console.log("All words:", translations.keys());
+// All words: [ 'hello', 'thank you', 'book', 'cat', 'computer' ]
+
+// Iterate through all translations
+translations.forEach((value, key) => {
+  console.log(`${key}: ${value}`);
+});
+
+
+// to see the output of this file use the command: node src/08-dictionary-hash/01-using-dictionary-class.js

src/08-dictionary-hash/02-using-map-class.js

@@ -0,0 +1,40 @@
+// src/08-dictionary-hash/02-using-map-class.js
+
+const translations = new Map();
+
+// Add some translations - English to Portuguese
+translations.set("hello", "olá"); 
+translations.set("thank you", "obrigado");
+translations.set("book", "livro");  
+translations.set("cat", "gato"); 
+translations.set("computer", "computador");
+
+// User interaction
+function translateWord(word) {
+  if (translations.has(word)) {
+    const translation = translations.get(word);
+    console.log(`The translation of "${word}" is "${translation}"`);
+  } else {
+    console.log(`Sorry, no translation found for "${word}"`);
+  }
+}
+
+// Example usage
+translateWord("hello"); // Output: The translation of "hello" is "olá"
+translateWord("dog");  // Output: Sorry, no translation found for "dog"
+
+// Get all translations
+console.log("All translations:", translations.values());
+// All translations: [ 'olá', 'obrigado', 'livro', 'gato', 'computador' ]
+
+// Get all words
+console.log("All words:", translations.keys());
+// All words: [ 'hello', 'thank you', 'book', 'cat', 'computer' ]
+
+// Iterate through all translations
+translations.forEach((value, key) => {
+  console.log(`${key}: ${value}`);
+});
+
+
+// to see the output of this file use the command: node src/08-dictionary-hash/01-using-dictionary-class.js

src/08-dictionary-hash/03-using-weakmap-class.js

@@ -0,0 +1,19 @@
+const privateData = new WeakMap();
+
+class Person {
+  constructor(name, age) {
+    this.name = name;
+    this.age = age;
+    privateData.set(this, { ssn: 'XXX-XX-XXXX', medicalHistory: [] });
+  }
+
+  getSSN() {
+    return privateData.get(this)?.ssn;
+  }
+}
+
+const alice = new Person("Penelope", 20);
+console.log(alice.name);      // Penelope
+console.log(alice.getSSN());  // XXX-XX-XXXX
+
+// Try to access private data

src/08-dictionary-hash/04-using-hashmap-class.js

@@ -0,0 +1,26 @@
+// src/08-dictionary-hash/04-using-hashmap-class.js
+
+const HashTable = require('./hash-table');
+
+const addressBook = new HashTable();
+
+// Add contacts
+addressBook.put('Gandalf', '[email protected]'); 
+addressBook.put('John', '[email protected]'); 
+addressBook.put('Tyrion', '[email protected]');
+
+// Retrieve the hash code of a contact
+console.log(addressBook.hash('Gandalf')); // 19
+console.log(addressBook.hash('John')); // 29
+console.log(addressBook.hash('Tyrion')); // 16
+
+// Retrieve contacts
+console.log(addressBook.get('Gandalf')); // gandalf@email.com
+console.log(addressBook.get('Loiane')); // undefined
+
+// Remove contacts
+console.log(addressBook.remove('Gandalf')); // true
+console.log(addressBook.get('Gandalf')); // undefined
+
+
+// to see the output of this file use the command: node src/08-dictionary-hash/04-using-hashmap-class.js

src/08-dictionary-hash/05-hashmap-collision.js

@@ -0,0 +1,42 @@
+// src/08-dictionary-hash/05-hashmap-collision.js
+
+const HashTable = require('./hash-table');
+
+const addressBook = new HashTable();
+
+// Add contacts
+addressBook.put('Ygritte', '[email protected]');
+addressBook.put('Jonathan', '[email protected]');
+addressBook.put('Jamie', '[email protected]');
+addressBook.put('Jack', '[email protected]');
+addressBook.put('Jasmine', '[email protected]');
+addressBook.put('Jake', '[email protected]');
+addressBook.put('Nathan', '[email protected]');
+addressBook.put('Athelstan', '[email protected]');
+addressBook.put('Sue', '[email protected]');
+addressBook.put('Aethelwulf', '[email protected]');
+addressBook.put('Sargeras', '[email protected]'); 
+
+// Retrieve the hash code of a contact
+console.log(addressBook.hash('Ygritte'), '- Ygritte'); // 4
+console.log(addressBook.hash('Jonathan'), '- Jonathan'); // 5
+console.log(addressBook.hash('Jamie'), '- Jamie'); // 5
+console.log(addressBook.hash('Jack'), '- Jack'); // 7
+console.log(addressBook.hash('Jasmine'), '- Jasmine'); // 8
+console.log(addressBook.hash('Jake'), '- Jake'); // 9
+console.log(addressBook.hash('Nathan'), '- Nathan'); // 10
+console.log(addressBook.hash('Athelstan'), '- Athelstan'); // 7
+console.log(addressBook.hash('Sue'), '- Sue'); // 5
+console.log(addressBook.hash('Aethelwulf'), '- Aethelwulf'); // 5
+console.log(addressBook.hash('Sargeras'), '- Sargeras'); // 10
+
+console.log(addressBook.toString());
+// {4 => ygritte@email.com}
+// {5 => aethelwulf@email.com}
+// {7 => athelstan@email.com}
+// {8 => jasmine@email.com}
+// {9 => jake@email.com}
+// {10 => sargeras@email.com}
+
+
+// to see the output of this file use the command: node src/08-dictionary-hash/05-hashmap-collision.js

src/08-dictionary-hash/dictionary.js

@@ -0,0 +1,59 @@
+// src/08-dictionary-hash/dictionary.js
+
+class Dictionary {
+  #items = {};
+  #size = 0;
+
+  hasKey(key) {
+    return this.#items[this.#elementToString(key)] != null;
+  }
+
+  set(key, value) {
+    if (key != null && value != null) {
+      const tableKey = this.#elementToString(key);
+      this.#items[tableKey] = value;
+      this.#size++;
+      return true;
+    }
+    return false;
+  }
+
+  delete(key) {
+    if (this.hasKey(key)) {
+      delete this.#items[this.#elementToString(key)];
+      this.#size--;
+      return true;
+    }
+    return false;
+  }
+
+  get(key) {
+    return this.#items[this.#elementToString(key)];
+  }
+
+  values() {
+    return Object.values(this.#items);
+  }
+
+  keys() {
+    return Object.keys(this.#items);
+  }
+
+  forEach(callbackFn) {
+    for (const key in this.#items) {
+      if (this.#items.hasOwnProperty(key)) {
+        callbackFn(this.#items[key], key);
+      }
+    }
+  }
+
+  #elementToString(data) {
+    if (typeof data === 'object' && data !== null) {
+      return JSON.stringify(data);
+    } else {
+      return data.toString(); 
+    }
+  }
+}
+
+module.exports = Dictionary;

src/08-dictionary-hash/hash-table-linear-probing.js

@@ -0,0 +1,101 @@
+// src/08-dictionary-hash/hash-table-linear-probing.js
+
+class HashTableLinearProbing {
+  #table = [];
+
+  #loseLoseHashCode(key) {
+    if (typeof key !== 'string') {
+      key = this.#elementToString(key);
+    }
+    const calcASCIIValue = (acc, char) => acc + char.charCodeAt(0);
+    const hash = key.split('').reduce((acc, char) => calcASCIIValue, 0);
+    return hash % 37; // mod to reduce the hash code
+  }
+
+  #djb2HashCode(key) {
+    if (typeof key !== 'string') {
+      key = this.#elementToString(key);
+    }
+    const calcASCIIValue = (acc, char) => (acc * 33) + char.charCodeAt(0);
+    const hash = key.split('').reduce((acc, char) => calcASCIIValue, 5381);
+    return hash % 1013;
+  } 
+
+  hash(key) {
+    return this.#loseLoseHashCode(key);
+  }
+
+  #elementToString(data) {
+    if (typeof data === 'object' && data !== null) {
+      return JSON.stringify(data);
+    } else {
+      return data.toString(); 
+    }
+  }
+
+  put(key, value) {
+    if (key != null && value != null) {
+      let index = this.hash(key);
+
+      // linear probing to find an empty slot
+      while (this.#table[index] != null) { 
+        if (this.#table[index].key === key) {
+          this.#table[index].value = value; // update existing key
+          return true;
+        }
+        index++;
+        index %= this.#table.length; // wrap around if end is reached
+      }
+
+      this.#table[index] = {key, value};
+      return true;
+    }
+    return false;
+  }
+
+  get(key) {
+    let index = this.hash(key);
+
+    // Linear probing to search for the key
+    while (this.#table[index] != null) {
+      if (this.#table[index].key === key) {
+        return this.#table[index].value;
+      }
+      index++;
+      index %= this.#table.length;
+    }
+
+    return undefined; // key not found
+  }
+
+  remove(key) {
+    let index = this.hash(key);
+    while (this.#table[index] != null) {
+      if (this.#table[index].key === key) {
+        delete this.#table[index];
+        this.#verifyRemoveSideEffect(key, index);
+        return true;
+      }
+      index++;
+      index %= this.#table.length;
+    }
+    return false; // key not found
+  }
+
+  #verifyRemoveSideEffect(key, removedPosition) {
+    const size = this.#table.length;
+    let index = removedPosition + 1; 
+    while (this.#table[index] != null) {
+      const currentKey = this.#table[index].key;
+      const currentHash = this.hash(currentKey);
+      // check if the element should be repositioned
+      if (currentHash <= removedPosition) { 
+        this.#table[removedPosition] = this.#table[index]; 
+        delete this.#table[index];
+        removedPosition = index; 
+      }
+      index++;
+      index %= size; // Wrap around if end is reached
+    }
+  }
+}