queue pic

README.md

@@ -3,6 +3,7 @@
 ## Content
 * [Stack](#stack)
 * [Set](#set)
+* [Queue](#queue)
 
 ### Stack <a name="stack"></a> 
 ![Stack](pics/stack.jpeg)
@@ -123,4 +124,30 @@ console.log(mySet2.list());                     // [ 'a', 'g', 'h' ]
 console.log(mySet.union(mySet2).list());        // [ 'a', 'b', 'g', 'h' ]
 console.log(mySet.intersect(mySet2).list());    // [ 'a' ]
 console.log(mySet.difference(mySet2).list());   // [ 'b', 'g', 'h' ]
+```
+
+
+### Queue <a name="queue"></a> 
+![Queue](pics/queue.jpg)
+```javascript
+    function Queue() { // first in, first out (FIFO)
+        const content = [];
+        this.list = function() { console.log(content) }; // list all queue item
+        this.enqueue = function(element) { content.push(element) }; // put item to the queue
+        this.dequeue = function() { return content.shift() }; // get the first item in the queue, remove it from the queue
+        this.front = function() { return content[0] }; // get the first item in the queue, still let it be in the queue
+        this.length = function() { return content.length }; // get queue length
+        this.isEmpty = function() { return (content.length == 0) } // check if queue is empty
+    }
+
+    const myQueue = new Queue();
+    myQueue.enqueue('a');            
+    myQueue.enqueue('b');           
+    myQueue.enqueue('c');           
+    myQueue.list();                 // [ 'a', 'b', 'c' ]
+    console.log(myQueue.dequeue()); // a
+    console.log(myQueue.front());   // b
+    console.log(myQueue.length());  // 2
+    console.log(myQueue.isEmpty()); // false
+    myQueue.list();                 // [ 'b', 'c' ]
 ```