1. var MyQueue = function() {
    2.     this.inStack = [];
    3.     this.outStack = [];
    4. };
    6. MyQueue.prototype.push = function(x) {
    7.     this.inStack.push(x);
    8. };
    10. MyQueue.prototype.pop = function() {
    11.     if (!this.outStack.length) {
    12.         this.in2out();
    13.     }
    14.     return this.outStack.pop();
    15. };
    17. MyQueue.prototype.peek = function() {
    18.     if (!this.outStack.length) {
    19.         this.in2out();
    20.     }
    21.     return this.outStack[this.outStack.length - 1];
    22. };
    24. MyQueue.prototype.empty = function() {
    25.     return this.outStack.length === 0 && this.inStack.length === 0;
    26. };
    28. MyQueue.prototype.in2out = function() {
    29.     while (this.inStack.length) {
    30.         this.outStack.push(this.inStack.pop());
    31.     }
    32. }