feat(queue): implement queue

Gapur · Gapur · commit 75e03d148376 · 2019-12-05T00:26:49.000+06:00
diff --git a/data-structures/index.js b/data-structures/index.js
@@ -1,5 +1,7 @@
 const LinkedList = require('./linked-list');
+const Queue = require('./queue');
 
 module.exports = {
   LinkedList,
+  Queue,
 };
diff --git a/data-structures/queue/Queue.js b/data-structures/queue/Queue.js
@@ -0,0 +1,37 @@
+const LinkedList = require('../linked-list/LinkedList');
+
+module.exports = class Queue {
+  constructor() {
+    // We're going to implement Queue based on LinkedList since the two
+    // structures are quite similar. Namely, they both operate mostly on
+    // the elements at the beginning and the end. Compare enqueue/dequeue
+    // operations of Queue with append/deleteHead operations of LinkedList.
+    this.linkedList = new LinkedList();
+  }
+
+  isEmpty() {
+    return !this.linkedList.head;
+  }
+
+  peek() {
+    if (!this.linkedList.head) {
+      return null;
+    }
+
+    return this.linkedList.head.value;
+  }
+
+  enqueue(value) {
+    this.linkedList.append(value);
+  }
+
+  dequeue() {
+    const removedHead = this.linkedList.deleteHead();
+    return removedHead ? removedHead.value : null;
+  }
+
+  toString(callback) {
+    // Return string representation of the queue's linked list.
+    return this.linkedList.toString(callback);
+  }
+};
diff --git a/data-structures/queue/index.js b/data-structures/queue/index.js
@@ -0,0 +1,25 @@
+const Queue = require('./Queue');
+
+console.log('start Queue ------');
+
+const queue = new Queue();
+
+queue.enqueue(1);
+queue.enqueue(2);
+
+console.log(`after enqueue queue ${queue.toString()}`);
+
+queue.enqueue({ value: 'test1', key: 'key1' });
+queue.enqueue({ value: 'test2', key: 'key2' });
+
+console.log(`after enqueue queue ${queue.toString()}`);
+
+console.log(`after dequeue=${queue.dequeue().value} queue ${queue.toString()}`);
+
+const peek = queue.peek();
+
+console.log(`after peek=${peek} isEmpty=${queue.isEmpty()}`);
+
+console.log('end Queue -------');
+
+module.exports = () => console.log('Queue is done');
