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】

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

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