232. Implement Queue using Stacks

# 鲁棒性比较差，没有做任何的优化，一旦输入和调用不按照规矩来，就会出错了
# eg: pick或者pop的时候queue为空，就会报错了（这里的测试用例都是按规矩调用的）
class MyQueue(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.queue = []
        

    def push(self, x):
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: None
        """
        self.queue.append(x)


    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        return self.queue.pop(0)
        

    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        return self.queue[0]
        

    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        return len(self.queue) == 0


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