Add Stack.

README.md

@@ -4,9 +4,9 @@
 
 ## Data Structures
 
-- [Linked List](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/linked-list)
-- [Hash Table](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/hash-table)
-- [Queue](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/queue)
+1. [Linked List](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/linked-list)
+2. [Queue](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/queue)
+3. [Hash Table](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/hash-table)
 
 ## Running Tests
 

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

@@ -160,6 +160,23 @@ export default class LinkedList {
     return deletedTail;
   }
 
+  deleteHead() {
+    if (!this.head) {
+      return null;
+    }
+
+    const deletedHead = this.head;
+
+    if (this.head.next) {
+      this.head = this.head.next;
+    } else {
+      this.head = null;
+      this.tail = null;
+    }
+
+    return deletedHead;
+  }
+
   findByKey(key) {
     let currentNode = this.head;
 

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

@@ -43,6 +43,8 @@ describe('LinkedList', () => {
   it('should delete node by value from linked list', () => {
     const linkedList = new LinkedList();
 
+    expect(linkedList.deleteByValue(5)).toBeNull();
+
     linkedList.append({ value: 1 });
     linkedList.append({ value: 2 });
     linkedList.append({ value: 3 });
@@ -80,55 +82,103 @@ describe('LinkedList', () => {
     expect(linkedList.tail.toString()).toBe('2');
   });
 
+  it('should delete node by key from linked list', () => {
+    const linkedList = new LinkedList();
+
+    expect(linkedList.deleteByKey('key')).toBeNull();
+
+    linkedList.append({ value: 1, key: 'test1' });
+    linkedList.append({ value: 2, key: 'test2' });
+    linkedList.append({ value: 3, key: 'test3' });
+    linkedList.append({ value: 4, key: 'test4' });
+
+    const deletedNode1 = linkedList.deleteByKey('test2');
+    expect(deletedNode1.key).toBe('test2');
+    expect(linkedList.toString()).toBe('test1:1,test3:3,test4:4');
+
+    const deletedNode2 = linkedList.deleteByKey('test1');
+    expect(deletedNode2.key).toBe('test1');
+    expect(linkedList.toString()).toBe('test3:3,test4:4');
+
+    const deletedNode3 = linkedList.deleteByKey('test4');
+    expect(deletedNode3.key).toBe('test4');
+    expect(linkedList.toString()).toBe('test3:3');
+  });
+
   it('should delete linked list tail', () => {
     const linkedList = new LinkedList();
 
+    linkedList.append({ value: 1 });
+    linkedList.append({ value: 2 });
+    linkedList.append({ value: 3 });
+
+    expect(linkedList.head.toString()).toBe('1');
+    expect(linkedList.tail.toString()).toBe('3');
+
+    const deletedNode1 = linkedList.deleteTail();
+
+    expect(deletedNode1.value).toBe(3);
+    expect(linkedList.toString()).toBe('1,2');
+    expect(linkedList.head.toString()).toBe('1');
+    expect(linkedList.tail.toString()).toBe('2');
+
+    const deletedNode2 = linkedList.deleteTail();
+
+    expect(deletedNode2.value).toBe(2);
+    expect(linkedList.toString()).toBe('1');
+    expect(linkedList.head.toString()).toBe('1');
+    expect(linkedList.tail.toString()).toBe('1');
+
+    const deletedNode3 = linkedList.deleteTail();
+
+    expect(deletedNode3.value).toBe(1);
+    expect(linkedList.toString()).toBe('');
+    expect(linkedList.head).toBeNull();
+    expect(linkedList.tail).toBeNull();
+  });
+
+  it('should delete linked list head', () => {
+    const linkedList = new LinkedList();
+
+    expect(linkedList.deleteHead()).toBeNull();
+
     linkedList.append({ value: 1 });
     linkedList.append({ value: 2 });
 
     expect(linkedList.head.toString()).toBe('1');
     expect(linkedList.tail.toString()).toBe('2');
 
-    const deletedNode1 = linkedList.deleteTail();
+    const deletedNode1 = linkedList.deleteHead();
 
-    expect(deletedNode1.value).toBe(2);
-    expect(linkedList.toString()).toBe('1');
-    expect(linkedList.head.toString()).toBe('1');
-    expect(linkedList.tail.toString()).toBe('1');
+    expect(deletedNode1.value).toBe(1);
+    expect(linkedList.toString()).toBe('2');
+    expect(linkedList.head.toString()).toBe('2');
+    expect(linkedList.tail.toString()).toBe('2');
 
-    const deletedNode2 = linkedList.deleteTail();
+    const deletedNode2 = linkedList.deleteHead();
 
-    expect(deletedNode2.value).toBe(1);
+    expect(deletedNode2.value).toBe(2);
     expect(linkedList.toString()).toBe('');
     expect(linkedList.head).toBeNull();
     expect(linkedList.tail).toBeNull();
   });
 
-  it('should delete node by key from linked list', () => {
-    const linkedList = new LinkedList();
-
-    linkedList.append({ value: 1, key: 'test1' });
-    linkedList.append({ value: 2, key: 'test2' });
-    linkedList.append({ value: 3, key: 'test3' });
-
-    const deletedNode = linkedList.deleteByKey('test2');
-    expect(deletedNode.key).toBe('test2');
-    expect(linkedList.toString()).toBe('test1:1,test3:3');
-  });
-
   it('should append unique nodes', () => {
     const linkedList = new LinkedList();
 
     linkedList.appendUnique({ value: 1, key: 'test1' });
     linkedList.appendUnique({ value: 2, key: 'test2' });
     linkedList.appendUnique({ value: 3, key: 'test2' });
+    linkedList.appendUnique({ value: 5, key: 'test1' });
 
-    expect(linkedList.toString()).toBe('test1:1,test2:3');
+    expect(linkedList.toString()).toBe('test1:5,test2:3');
   });
 
   it('should find node by its key', () => {
     const linkedList = new LinkedList();
 
+    expect(linkedList.findByKey('test')).toBeNull();
+
     linkedList.appendUnique({ value: 1, key: 'test1' });
     linkedList.appendUnique({ value: 2, key: 'test2' });
     linkedList.appendUnique({ value: 3, key: 'test3' });

src/data-structures/queue/Queue.js

@@ -10,19 +10,19 @@ export default class Queue {
   }
 
   peek() {
-    if (!this.linkedList.tail) {
+    if (!this.linkedList.head) {
       return null;
     }
 
-    return this.linkedList.tail.value;
+    return this.linkedList.head.value;
   }
 
-  add(value) {
+  enqueue(value) {
     this.linkedList.append({ value });
   }
 
-  remove() {
-    const removedTail = this.linkedList.deleteTail();
-    return removedTail ? removedTail.value : null;
+  dequeue() {
+    const removedHead = this.linkedList.deleteHead();
+    return removedHead ? removedHead.value : null;
   }
 }

src/data-structures/queue/README.md

@@ -1,8 +1,2 @@
 # Queue
 
-|Operation                  |Complexity         |
-|---------------------------|-------------------|
-|Find                       |O()               |
-|Insert/delete at beginning |O()               |
-|Insert/delete in middle    |O() |
-|Insert/delete at end       |O() |

src/data-structures/queue/__test__/Queue.test.js

@@ -7,11 +7,11 @@ describe('Queue', () => {
     expect(queue.linkedList).not.toBeNull();
   });
 
-  it('should add data to queue', () => {
+  it('should enqueue data to queue', () => {
     const queue = new Queue();
 
-    queue.add(1);
-    queue.add(2);
+    queue.enqueue(1);
+    queue.enqueue(2);
 
     expect(queue.linkedList.toString()).toBe('1,2');
   });
@@ -21,11 +21,11 @@ describe('Queue', () => {
 
     expect(queue.peek()).toBeNull();
 
-    queue.add(1);
-    queue.add(2);
+    queue.enqueue(1);
+    queue.enqueue(2);
 
-    expect(queue.peek()).toBe(2);
-    expect(queue.peek()).toBe(2);
+    expect(queue.peek()).toBe(1);
+    expect(queue.peek()).toBe(1);
   });
 
   it('should check if queue is empty', () => {
@@ -33,19 +33,19 @@ describe('Queue', () => {
 
     expect(queue.isEmpty()).toBeTruthy();
 
-    queue.add(1);
+    queue.enqueue(1);
 
     expect(queue.isEmpty()).toBeFalsy();
   });
 
-  it('should remove from empty', () => {
+  it('should dequeue from queue in FIFO order', () => {
     const queue = new Queue();
 
-    queue.add(1);
-    queue.add(2);
+    queue.enqueue(1);
+    queue.enqueue(2);
 
-    expect(queue.remove()).toBe(2);
-    expect(queue.remove()).toBe(1);
+    expect(queue.dequeue()).toBe(1);
+    expect(queue.dequeue()).toBe(2);
     expect(queue.isEmpty()).toBeTruthy();
   });
 });

src/data-structures/stack/README.md

@@ -0,0 +1 @@
+# Queue

src/data-structures/stack/Stack.js

@@ -0,0 +1,28 @@
+import LinkedList from '../linked-list/LinkedList';
+
+export default class Stack {
+  constructor() {
+    this.linkedList = new LinkedList();
+  }
+
+  isEmpty() {
+    return !this.linkedList.tail;
+  }
+
+  peek() {
+    if (!this.linkedList.tail) {
+      return null;
+    }
+
+    return this.linkedList.tail.value;
+  }
+
+  push(value) {
+    this.linkedList.append({ value });
+  }
+
+  pop() {
+    const removedTail = this.linkedList.deleteTail();
+    return removedTail ? removedTail.value : null;
+  }
+}

src/data-structures/stack/__test__/Stack.test.js

@@ -0,0 +1,51 @@
+import Stack from '../Stack';
+
+describe('Stack', () => {
+  it('should create empty stack', () => {
+    const stack = new Stack();
+    expect(stack).not.toBeNull();
+    expect(stack.linkedList).not.toBeNull();
+  });
+
+  it('should stack data to stack', () => {
+    const stack = new Stack();
+
+    stack.push(1);
+    stack.push(2);
+
+    expect(stack.linkedList.toString()).toBe('1,2');
+  });
+
+  it('should peek data from stack', () => {
+    const stack = new Stack();
+
+    expect(stack.peek()).toBeNull();
+
+    stack.push(1);
+    stack.push(2);
+
+    expect(stack.peek()).toBe(2);
+    expect(stack.peek()).toBe(2);
+  });
+
+  it('should check if stack is empty', () => {
+    const stack = new Stack();
+
+    expect(stack.isEmpty()).toBeTruthy();
+
+    stack.push(1);
+
+    expect(stack.isEmpty()).toBeFalsy();
+  });
+
+  it('should pop data from stack', () => {
+    const stack = new Stack();
+
+    stack.push(1);
+    stack.push(2);
+
+    expect(stack.pop()).toBe(2);
+    expect(stack.pop()).toBe(1);
+    expect(stack.isEmpty()).toBeTruthy();
+  });
+});