[leetcode: Python]232. Implement Queue using Stacks

题目：
Implement the following operations of a queue using stacks.

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

方法一：性能39ms

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: void        """        self.queue.append(x)    def pop(self):        """        Removes the element from in front of queue and returns that element.        :rtype: int        """        if not self.empty():            return self.queue.pop(0)    def peek(self):        """        Get the front element.        :rtype: int        """        if not self.empty():            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()

方法二：性能32ms

    def push(self, x):        self.stack.append(x)        self.curElements += 1        """        Push element x to the back of queue.        :type x: int        :rtype: void        """    def pop(self):        res = self.stack[self.curFront]        self.curFront += 1        self.curElements -= 1        return res        """        Removes the element from in front of queue and returns that element.        :rtype: int        """    def peek(self):        return self.stack[self.curFront]        """        Get the front element.        :rtype: int        """    def empty(self):        return self.curElements == 0        """        Returns whether the queue is empty.        :rtype: bool        """# 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()