数据结构 之 栈与队列

Posted 2021-02-13 donghaoblogs

栈

 

队列

栈的实现

 

顺序表实现

 

class Stack(object):
    """栈"""
    def __init__(self):
        self.__list = []  # 选用顺序表或链表

    def push(self,item):
        """压栈"""
        self.__list.append(item) # 时间复杂度O(1)
        self.__list.insert(0,item) #头部插入，时间复杂度O(n)

        # 说明：链表结构的话，头部插入。

    def pop(self):
        return self.__list.pop()
        # return self.__list[0]  #时间复杂度 O(n)

    def peek(self):
        """返回栈顶元素"""
        if self.__list:  #不为空
            return self.__list[-1]
        else:
            return None

    def is_empty(self):
        """是否为空"""
        return not self.__list


    def size(self):
        return len(self.__list)


if __name__ == ‘__main__‘:
    s = Stack()
    s.push(1)
    s.push(3)
    s.push(4)
    s.push(5)
    s.push(6)
    print(s.pop())
    print(s.pop())
    print(s.pop())
    print(s.pop())

换个姿势，链表实现 队列

import queue

class Node(object):
    def __init__(self,item):
        self.item = item
        self.next = None

class Queue(object):
    """队列"""
    def __init__(self,node=None):
        self._head = node

    def enqueue(self,item):
        """入队"""
        node = Node(item)
        node.next = self._head
        self._head = node

    def dequeue(self):
        """出队"""
        cur = self._head
        pre = None
        while cur.next!= None:
            pre = cur
            cur = cur.next
        if cur is self._head:  
            self._head = cur.next
            return cur.item
        pre.next = None
        return cur.item

    def is_empty(self):
        """判断是否为空"""
        return self._head == None

    def size(self):
        cur = self._head
        index = 0
        while cur!= None:
            cur = cur.next
            index+=1
        return index

双端队列

操作：

#encoding:utf-8
# __author__ = ‘donghao‘
# __time__ = 2019/3/16 17:17

class Deque(object):
    def __init__(self):
        self._list = []

    def add_front(self,item):
        self._list.insert(0,item)

    def add_end(self,item):
        self._list.append(item)

    def pop_front(self):
        return self._list.pop(0)

    def pop_end(self):
        return self._list.pop()

    def size(self):
        return len(self._list)

    def is_empty(self):
        return self._list == []

if __name__ == ‘__main__‘:
    que = Deque()
    que.add_end(1)
    que.add_end(2)   # [6,5,4,1,2,3]
    que.add_end(3)
    que.add_front(4)
    que.add_front(5)
    que.add_front(6)
    print(que.pop_front())
    print(que.pop_end())
    print(que.pop_end())
    print(que.pop_end())