[LeetCode][JavaScript]Implement Queue using Stacks

 1 /**
 2  * @constructor
 3  */
 4 var Queue = function() {
 5     this.stack1 = [];
 6     this.stack2 = [];
 7 };
 8 
 9 /**
10  * @param {number} x
11  * @returns {void}
12  */
13 Queue.prototype.push = function(x) {
14     var len = this.stack2.length;
15     while(len--){
16         this.stack1.push(this.stack2.pop());
17     }
18     this.stack1.push(x);
19 };
20 
21 /**
22  * @returns {void}
23  */
24 Queue.prototype.pop = function() {
25     if(this.stack2.length === 0){
26         var len = this.stack1.length;
27         while(len--){
28             this.stack2.push(this.stack1.pop());
29         }
30     }
31     return this.stack2.pop();
32 };
33 
34 /**
35  * @returns {number}
36  */
37 Queue.prototype.peek = function() {
38     if(this.stack2.length === 0){
39         var len = this.stack1.length;
40         while(len--){
41             this.stack2.push(this.stack1.pop());
42         }
43     }
44     return this.stack2[this.stack2.length - 1];
45 };
46 
47 /**
48  * @returns {boolean}
49  */
50 Queue.prototype.empty = function() {
51     if(this.stack1.length === 0 && this.stack2.length === 0){
52         return true;
53     }
54     return false;
55 };