python

超轻量级php框架startmvc

Python数据结构与算法之链表定义与用法实例详解【单链表、循环链表】

更新时间:2020-05-08 06:36:01 作者:startmvc
本文实例讲述了Python数据结构与算法之链表定义与用法。分享给大家供大家参考,具体如下

本文实例讲述了Python数据结构与算法之链表定义与用法。分享给大家供大家参考,具体如下:

本文将为大家讲解:

(1)从链表节点的定义开始,以类的方式,面向对象的思想进行链表的设计

(2)链表类插入和删除等成员函数实现时需要考虑的边界条件, prepend(头部插入)、pop(头部删除)、append(尾部插入)、pop_last(尾部删除)

2.1 插入:

空链表 链表长度为1 插入到末尾

2.2 删除

空链表 链表长度为1 删除末尾元素

(3)从单链表到单链表的一众变体:

带尾节点的单链表 循环单链表 双链表

1. 链表节点的定义


class LNode:
 def __init__(self, elem, next_=None):
 self.elem = elem
 self.next = next_

2. 单链表的实现

重点理解插入、删除的实现及其需要考虑的边界条件:


class LinkedListUnderflow(ValueError):
 pass
class LList:
 def __init__(self):
 self._head = None
 def is_empty(self):
 return self._head is None
 def prepend(self, elem):
 self._head = LNode(elem, self._head)
 def pop(self):
 if self._head is None:
 raise LinkedListUnderflow('in pop')
 e = self._head.elem
 self._head = self._head.next
 return e
 def append(self, elem):
 if self._head is None:
 self._head = LNode(elem)
 return
 p = self._head
 while p.next is not None:
 p = p.next
 p.next = LNode(elem)
 def pop_last(self):
 if self._head is None:
 raise LinkedListUnderflow('in pop_last')
 p = self._head
 if p.next is None:
 e = p.elem
 self._head = None
 return e
 while p.next.next is not None:
 p = p.next
 e = p.next.elem
 p.next = None
 return e

简单总结:

(0)能够访问 p.next.next 的前提是 p.next 不为空; (1)尾部插入,如果链表不为空,需且仅需改变的是尾部节点的指针; (2)尾部删除,如果链表长度不为空,需且仅需改变的是倒数第二个节点的指针。

单链表的简单变形:具有尾部节点的单链表


class LList1(LList):
 def __init__(self):
 LList.__init__(self)
 self._rear = None
 ...

我们仅需重写的是:头部的插入、尾部的插入、尾部的删除


def prepend(self, elem):
 if self._head is None:
 self._head = LNode(elem)
 self._rear = self._head
 else:
 self._head = LNode(elem, self._head)
def append(self, elem):
 if self._head is None:
 self._head = LNode(elem)
 self._rear = self._head
 else:
 self._rear.next = LNode(elem)
 self._rear = self._rear.next
def pop_last(self):
 if self._head is None:
 raise LinkedListUnderflow('in pop_last')
 p = self._head
 if p.next is None:
 e = p.elem
 self._head = None
 return e
 while p.next.next is not None:
 p = p.next
 e = p.next.elem
 self._rear = p
 p.next = None
 return e

单链表的变体:循环单链表


class LCList:
 def __init__(self):
 self._rear = None
 def prepend(self, elem):
 if self._rear is None:
 self._rear = LNode(elem)
 self._rear.next = self._rear
 else:
 self._rear.next = LNode(elem, self._rear.next)
 def append(self, elem):
 self.prepend(elem)
 self_rear = self._rear.next
 def pop(self):
 if self._rear is None:
 raise LinkedListUnderflow('in pop')
 p = self._rear.next
 if p is None:
 self._rear = None
 else:
 self._rear.next = p.next
 return p.elem
 def printall(self):
 if self._rear is None:
 raise ...
 p = self._rear.next
 while True:
 print(p.elem)
 if p is self._rear:
 break
 p = p.next

Python 数据结构 算法 链表 单链表、循环链表