Detailed introduction to the linked list of python data structure-Python Tutorial-php.cn

This article mainly introduces the relevant information of the Python data structure linked list in detail, which has certain reference value. Interested friends can refer to it

Data structure is a must master in computer science As a subject, many previous textbooks used C language to implement linked lists. Because C has pointers, it can easily control memory and implement linked lists. Other languages are not so convenient. Many use simulated linked lists. , but this time, I did not use a simulated linked list to implement it, because Python is a dynamic language and can directly assign objects to new variables.

Okay, before I talk about my implementation in python, let me briefly talk about the linked list. When we store a large wave of data, we often use arrays, but it is very troublesome when we perform insertion operations. Look at the example below. There is a bunch of data 1, 2, 3, 5, 6, 7. We want to insert it into 3 Insert 4 between 5 and 5. What will we do if we use an array? Of course, the data after 5 is moved back one position, and then 4 is inserted. This is very troublesome, but if I use a linked list, I can just insert 4 directly between 3 and 5, which sounds very convenient.

So what is the structure of the linked list? As the name suggests, a linked list is of course like a chain, with nodes connected together to form a data chain.

The node structure of the linked list is as follows:

data is the customized data, and next is the address of the next node.

The structure of the linked list is, head saves the address of the first node:

Next we will use python to implement the linked list

Python implements linked list

First, define the node class Node:

class Node:
  &#39;&#39;&#39;
  data: 节点保存的数据
  _next: 保存下一个节点对象
  &#39;&#39;&#39;
  def __init__(self, data, pnext=None):
    self.data = data
    self._next = pnext

  def __repr__(self):
    &#39;&#39;&#39;
    用来定义Node的字符输出，
    print为输出data
    &#39;&#39;&#39;
    return str(self.data)

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Then, define the linked list class:

The linked list must include :

Attributes:

Linked list header: head

Linked list length: length

Method:

Judge whether it is empty: isEmpty( )

def isEmpty(self):
  return (self.length == 0

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Add a node (add at the end of the linked list): append()

def append(self, dataOrNode):
  item = None
  if isinstance(dataOrNode, Node):
    item = dataOrNode
  else:
    item = Node(dataOrNode)

  if not self.head:
    self.head = item
    self.length += 1

  else:
    node = self.head
    while node._next:
      node = node._next
    node._next = item
    self.length += 1

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Delete a node: delete()

#删除一个节点之后记得要把链表长度减一
def delete(self, index):
  if self.isEmpty():
    print "this chain table is empty."
    return

  if index < 0 or index >= self.length:
    print &#39;error: out of index&#39;
    return
  #要注意删除第一个节点的情况
  #如果有空的头节点就不用这样
  #但是我不喜欢弄头节点
  if index == 0:
    self.head = self.head._next
    self.length -= 1
    return

  #prev为保存前导节点
  #node为保存当前节点
  #当j与index相等时就
  #相当于找到要删除的节点
  j = 0
  node = self.head
  prev = self.head
  while node._next and j < index:
    prev = node
    node = node._next
    j += 1

  if j == index:
    prev._next = node._next
    self.length -= 1

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Modify a node: update()

def update(self, index, data):
  if self.isEmpty() or index < 0 or index >= self.length:
    print &#39;error: out of index&#39;
    return
  j = 0
  node = self.head
  while node._next and j < index:
    node = node._next
    j += 1

  if j == index:
    node.data = data

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Find a node: getItem()

def getItem(self, index):
  if self.isEmpty() or index < 0 or index >= self.length:
    print "error: out of index"
    return
  j = 0
  node = self.head
  while node._next and j < index:
    node = node._next
    j += 1

  return node.data

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Find the index of a node: getIndex()

def getIndex(self, data):
  j = 0
  if self.isEmpty():
    print "this chain table is empty"
    return
  node = self.head
  while node:
    if node.data == data:
      return j
    node = node._next
    j += 1

  if j == self.length:
    print "%s not found" % str(data)
    return

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Insert a node: insert()

def insert(self, index, dataOrNode):
  if self.isEmpty():
    print "this chain tabale is empty"
    return

  if index < 0 or index >= self.length:
    print "error: out of index"
    return

  item = None
  if isinstance(dataOrNode, Node):
    item = dataOrNode
  else:
    item = Node(dataOrNode)

  if index == 0:
    item._next = self.head
    self.head = item
    self.length += 1
    return

  j = 0
  node = self.head
  prev = self.head
  while node._next and j < index:
    prev = node
    node = node._next
    j += 1

  if j == index:
    item._next = node
    prev._next = item
    self.length += 1

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Clear the linked list: clear()

def clear(self):
  self.head = None
  self.length = 0

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The above is the method to be implemented in the linked list class.

Result of execution:

#The following is the complete code:

# -*- coding:utf8 -*-
#/usr/bin/env python

class Node(object):
 def __init__(self, data, pnext = None):
  self.data = data
  self._next = pnext

 def __repr__(self):
  return str(self.data)

class ChainTable(object):
 def __init__(self):
  self.head = None
  self.length = 0

 def isEmpty(self):
  return (self.length == 0)

 def append(self, dataOrNode):
  item = None
  if isinstance(dataOrNode, Node):
   item = dataOrNode
  else:
   item = Node(dataOrNode)

  if not self.head:
   self.head = item
   self.length += 1

  else:
   node = self.head
   while node._next:
    node = node._next
   node._next = item
   self.length += 1

 def delete(self, index):
  if self.isEmpty():
   print "this chain table is empty."
   return

  if index < 0 or index >= self.length:
   print &#39;error: out of index&#39;
   return

  if index == 0:
   self.head = self.head._next
   self.length -= 1
   return

  j = 0
  node = self.head
  prev = self.head
  while node._next and j < index:
   prev = node
   node = node._next
   j += 1

  if j == index:
   prev._next = node._next
   self.length -= 1

 def insert(self, index, dataOrNode):
  if self.isEmpty():
   print "this chain tabale is empty"
   return

  if index < 0 or index >= self.length:
   print "error: out of index"
   return

  item = None
  if isinstance(dataOrNode, Node):
   item = dataOrNode
  else:
   item = Node(dataOrNode)

  if index == 0:
   item._next = self.head
   self.head = item
   self.length += 1
   return

  j = 0
  node = self.head
  prev = self.head
  while node._next and j < index:
   prev = node
   node = node._next
   j += 1

  if j == index:
   item._next = node
   prev._next = item
   self.length += 1

 def update(self, index, data):
  if self.isEmpty() or index < 0 or index >= self.length:
   print &#39;error: out of index&#39;
   return
  j = 0
  node = self.head
  while node._next and j < index:
   node = node._next
   j += 1

  if j == index:
   node.data = data

 def getItem(self, index):
  if self.isEmpty() or index < 0 or index >= self.length:
   print "error: out of index"
   return
  j = 0
  node = self.head
  while node._next and j < index:
   node = node._next
   j += 1

  return node.data


 def getIndex(self, data):
  j = 0
  if self.isEmpty():
   print "this chain table is empty"
   return
  node = self.head
  while node:
   if node.data == data:
    return j
   node = node._next
   j += 1

  if j == self.length:
   print "%s not found" % str(data)
   return

 def clear(self):
  self.head = None
  self.length = 0

 def __repr__(self):
  if self.isEmpty():
   return "empty chain table"
  node = self.head
  nlist = &#39;&#39;
  while node:
   nlist += str(node.data) + &#39; &#39;
   node = node._next
  return nlist

 def __getitem__(self, ind):
  if self.isEmpty() or ind < 0 or ind >= self.length:
   print "error: out of index"
   return
  return self.getItem(ind)

 def __setitem__(self, ind, val):
  if self.isEmpty() or ind < 0 or ind >= self.length:
   print "error: out of index"
   return
  self.update(ind, val)

 def __len__(self):
  return self.length

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