[leetcode: Python]225. Implement Stack using Queues

题目：
mplement the following operations of a stack using queues.

push(x) – Push element x onto stack.
pop() – Removes the element on top of the stack.
top() – Get the top element.
empty() – Return whether the stack is empty.
Notes:
You must use only standard operations of a queue – which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

方法一：性能45ms

class MyStack(object):

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

    def push(self, x):
        """
        Push element x onto stack.
        :type x: int
        :rtype: void
        """

        self.myStack.append(x)


    def pop(self):
        """
        Removes the element on top of the stack and returns that element.
        :rtype: int
        """
        if not self.empty():
            return self.myStack.pop()


    def top(self):
        """
        Get the top element.
        :rtype: int
        """
        if not self.empty():
            return self.myStack[-1]


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




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

方法二：性能32ms

class MyStack(object):

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

    def push(self, x):
        """
        Push element x onto stack.
        :type x: int
        :rtype: void
        """
        self.queue.append(x)


    def pop(self):
        """
        Removes the element on top of the stack and returns that element.
        :rtype: int
        """
        _queue = self.queue
        for _ in range(len(_queue)-1):
            _queue.append(_queue.pop(0))
        return _queue.pop(0)


    def top(self):
        """
        Get the top element.
        :rtype: int
        """
        tmp = self.pop()
        self.queue.append(tmp)
        return tmp


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



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