232. 用栈实现队列

使用栈实现队列的下列操作：

push(x) -- 将一个元素放入队列的尾部。
pop() -- 从队列首部移除元素。
peek() -- 返回队列首部的元素。
empty() -- 返回队列是否为空。

示例:
MyQueue queue = new MyQueue();
queue.push(1);
queue.push(2);
queue.peek(); // 返回 1
queue.pop(); // 返回 1
queue.empty(); // 返回 false

题解

/**
 * Initialize your data structure here.
 */
var MyQueue = function() {
    this.stack=[]
    this.temp=[]
};

/**
 * Push element x to the back of queue. 
 * @param {number} x
 * @return {void}
 */
MyQueue.prototype.push = function(x) {
    if(this.stack.length==0){
       this.stack.push(x)
    }else{
        while(this.stack.length > 0) {
            this.temp.push(this.stack.pop());
        }
        this.stack.push(x);
        while(this.temp.length > 0) {
            this.stack.push(this.temp.pop());
        }
    }
    return this.stack
};

/**
 * Removes the element from in front of queue and returns that element.
 * @return {number}
 */
MyQueue.prototype.pop = function() {
    return this.stack.pop()
};

/**
 * Get the front element.
 * @return {number}
 */
MyQueue.prototype.peek = function() {
    return this.stack[this.stack.length-1]
};

/**
 * Returns whether the queue is empty.
 * @return {boolean}
 */
MyQueue.prototype.empty = function() {
    return this.stack.length==0
};

/** 
 * Your MyQueue object will be instantiated and called as such:
 * var obj = new MyQueue()
 * obj.push(x)
 * var param_2 = obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.empty()
 */