Make it possible to add objects to LinkedList.

Author: trekhleb

src/data-structures/hash-table/HashTable.js

@@ -21,16 +21,32 @@ export default class HashTable {
 
   insert(key, value) {
     const bucketLinkedList = this.buckets[this.hash(key)];
-    bucketLinkedList.appendUnique({ key, value });
+    const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
+
+    if (!node) {
+      // Insert new node.
+      bucketLinkedList.append({ key, value });
+    } else {
+      // Update value of existing node.
+      node.value.value = value;
+    }
   }
 
   delete(key) {
     const bucketLinkedList = this.buckets[this.hash(key)];
-    return bucketLinkedList.deleteByKey(key);
+    const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
+
+    if (node) {
+      return bucketLinkedList.delete(node.value);
+    }
+
+    return null;
   }
 
   get(key) {
     const bucketLinkedList = this.buckets[this.hash(key)];
-    return bucketLinkedList.findByKey(key);
+    const node = bucketLinkedList.find({ callback: nodeValue => nodeValue.key === key });
+
+    return node ? node.value.value : null;
   }
 }

src/data-structures/hash-table/__test__/HashTable.test.js

@@ -31,19 +31,34 @@ describe('HashTable', () => {
     hashTable.insert('c', 'earth');
     hashTable.insert('d', 'ocean');
 
-    expect(hashTable.buckets[0].toString()).toBe('c:earth');
-    expect(hashTable.buckets[1].toString()).toBe('a:sky,d:ocean');
-    expect(hashTable.buckets[2].toString()).toBe('b:sea');
+    const stringifier = value => `${value.key}:${value.value}`;
 
-    expect(hashTable.get('a').value).toBe('sky');
-    expect(hashTable.get('d').value).toBe('ocean');
+    expect(hashTable.buckets[0].toString(stringifier)).toBe('c:earth');
+    expect(hashTable.buckets[1].toString(stringifier)).toBe('a:sky,d:ocean');
+    expect(hashTable.buckets[2].toString(stringifier)).toBe('b:sea');
+
+    expect(hashTable.get('a')).toBe('sky');
+    expect(hashTable.get('d')).toBe('ocean');
 
     hashTable.delete('a');
 
+    expect(hashTable.delete('not-existing')).toBeNull();
+
     expect(hashTable.get('a')).toBeNull();
-    expect(hashTable.get('d').value).toBe('ocean');
+    expect(hashTable.get('d')).toBe('ocean');
 
     hashTable.insert('d', 'ocean-new');
-    expect(hashTable.get('d').value).toBe('ocean-new');
+    expect(hashTable.get('d')).toBe('ocean-new');
+  });
+
+  it('should be possible to add objects to hash table', () => {
+    const hashTable = new HashTable();
+
+    hashTable.insert('objectKey', { prop1: 'a', prop2: 'b' });
+
+    const object = hashTable.get('objectKey');
+    expect(object).toBeDefined();
+    expect(object.prop1).toBe('a');
+    expect(object.prop2).toBe('b');
   });
 });

src/data-structures/linked-list/LinkedList.js

@@ -2,74 +2,39 @@ import LinkedListNode from './LinkedListNode';
 
 export default class LinkedList {
   constructor() {
+    /** @var LinkedListNode */
     this.head = null;
+
+    /** @var LinkedListNode */
     this.tail = null;
   }
 
-  prepend({ value, key = null }) {
-    const newNode = new LinkedListNode({ value, key, next: this.head });
-
+  prepend(value) {
     // Make new node to be a head.
-    this.head = newNode;
+    this.head = new LinkedListNode(value, this.head);
 
-    return newNode;
+    return this;
   }
 
-  append({ value, key = null }) {
-    const newNode = new LinkedListNode({ value, key });
+  append(value) {
+    const newNode = new LinkedListNode(value);
 
     // If there is no head yet let's make new node a head.
     if (!this.head) {
       this.head = newNode;
       this.tail = newNode;
 
-      return newNode;
+      return this;
     }
 
     // Attach new node to the end of linked list.
     this.tail.next = newNode;
     this.tail = newNode;
 
-    return newNode;
+    return this;
   }
 
-  appendUnique({ value, key = null }) {
-    const newNode = new LinkedListNode({ value, key });
-
-    // If there is no head yet let's make new node a head.
-    if (!this.head) {
-      this.head = newNode;
-      this.tail = newNode;
-
-      return newNode;
-    }
-
-    // Rewind to last node.
-    let currentNode = this.head;
-    while (currentNode.next !== null) {
-      // If there is a node with specified key exists then update it instead of adding new one.
-      if (key && currentNode.key === key) {
-        currentNode.value = value;
-        return currentNode;
-      }
-
-      currentNode = currentNode.next;
-    }
-
-    // If there is a node with specified key exists then update it instead of adding new one.
-    if (key && currentNode.key === key) {
-      currentNode.value = value;
-      return currentNode;
-    }
-
-    // Attach new node to the end of linked list.
-    currentNode.next = newNode;
-    this.tail = newNode;
-
-    return newNode;
-  }
-
-  deleteByValue(value) {
+  delete(value) {
     if (!this.head) {
       return null;
     }
@@ -102,37 +67,28 @@ export default class LinkedList {
     return deletedNode;
   }
 
-  deleteByKey(key) {
+  find({ value = undefined, callback = undefined }) {
     if (!this.head) {
       return null;
     }
 
-    let deletedNode = null;
-
-    // If the head must be deleted then make 2nd node to be a head.
-    if (this.head.key === key) {
-      deletedNode = this.head;
-      this.head = this.head.next;
-    }
-
     let currentNode = this.head;
 
-    // If next node must be deleted then make next node to be a next next one.
-    while (currentNode.next) {
-      if (currentNode.next.key === key) {
-        deletedNode = currentNode.next;
-        currentNode.next = currentNode.next.next;
-      } else {
-        currentNode = currentNode.next;
+    while (currentNode) {
+      // If callback is specified then try to find node by callback.
+      if (callback && callback(currentNode.value)) {
+        return currentNode;
       }
-    }
 
-    // Check if tail must be deleted.
-    if (this.tail.key === key) {
-      this.tail = currentNode;
+      // If value is specified then try to compare by value..
+      if (value !== undefined && currentNode.value === value) {
+        return currentNode;
+      }
+
+      currentNode = currentNode.next;
     }
 
-    return deletedNode;
+    return null;
   }
 
   deleteTail() {
@@ -177,32 +133,15 @@ export default class LinkedList {
     return deletedHead;
   }
 
-  findByKey(key) {
-    let currentNode = this.head;
+  toString(callback) {
+    const nodeStrings = [];
 
-    while (currentNode) {
-      if (currentNode.key === key) {
-        return currentNode;
-      }
-      currentNode = currentNode.next;
-    }
-
-    return null;
-  }
-
-  toArray() {
-    const listArray = [];
     let currentNode = this.head;
-
     while (currentNode) {
-      listArray.push(currentNode.toString());
+      nodeStrings.push(currentNode.toString(callback));
       currentNode = currentNode.next;
     }
 
-    return listArray;
-  }
-
-  toString() {
-    return this.toArray().toString();
+    return nodeStrings.toString();
   }
 }

src/data-structures/linked-list/LinkedListNode.js

@@ -1,17 +1,10 @@
 export default class LinkedListNode {
-  constructor({ value, next = null, key = null }) {
+  constructor(value, next = null) {
     this.value = value;
     this.next = next;
-
-    // Key is added to make this linked list nodes to be reusable in hash tables.
-    this.key = key;
   }
 
-  toString() {
-    if (this.key) {
-      return `${this.key}:${this.value}`;
-    }
-
-    return `${this.value}`;
+  toString(callback) {
+    return callback ? callback(this.value) : `${this.value}`;
   }
 }