python-035-循环链表实现栈

之前实现过栈，用过数组，用过链表，但有时候用循环链表能更快的满足我们的程序需要，但是最近要准备考试，就不说了

class Empty(Exception):
    pass


class CircularQueue:
    class _Node:
        def __init__(self, element, next):
            self._element = element
            self._next = next

    def __init__(self):
        self._tail = None
        self._size = 0

    def __len__(self):
        return self._size

    def is_empty(self):
        return self._size == 0

    def first(self):
        if self.is_empty():
            raise Empty("Queue is Empty！")
        return self._tail._next._elelment

    def enqueue(self, e):
        newest = self._Node(e, None)
        if self.is_empty():
            newest._next = newest
        else:
            newest._next = self._tail._next
        self._tail = newest
        self._size += 1

    def dequeue(self):
        if self.is_empty():
            raise Empty("Queue is Empty！")
        head = self._tail._next
        answer = head._element
        if self._size == 1:
            self.tail = None
        else:
            self._tail._next = head._next
        self._size -= 1
        return answer

    def rotate(self):
        if self._size > 0:
            self._tail = self._tail._next

先这样，如果之后有时间会把这个补上。