python数据结构之链表详解

数据结构是计算机科学必须掌握的一门学问，之前很多的教材都是用C语言实现链表，因为c有指针，可以很方便的控制内存，很方便就实现链表，其他的语言，则没那么方便，有很多都是用模拟链表，不过这次，我不是用模拟链表来实现，因为python是动态语言，可以直接把对象赋值给新的变量。

好了，在说我用python实现前，先简单说说链表吧。在我们存储一大波数据时，我们很多时候是使用数组，但是当我们执行插入操作的时候就是非常麻烦，看下面的例子，有一堆数据1,2,3,5,6,7我们要在3和5之间插入4,如果用数组，我们会怎么做？当然是将5之后的数据往后退一位，然后再插入4,这样非常麻烦，但是如果用链表，我就直接在3和5之间插入4就行，听着就很方便。

那么链表的结构是怎么样的呢？顾名思义，链表当然像锁链一样，由一节节节点连在一起，组成一条数据链。

链表的节点的结构如下：

data为自定义的数据，next为下一个节点的地址。

链表的结构为，head保存首位节点的地址：

接下来我们来用python实现链表

python实现链表

首先，定义节点类Node：

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

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

然后，定义链表类：

链表要包括：

属性：

链表头：head

链表长度：length

方法：

判断是否为空: isEmpty()

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

增加一个节点(在链表尾添加): 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

删除一个节点: 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 'error: out of index'
    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

修改一个节点: update()

def update(self, index, data):
  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

  if j == index:
    node.data = data

查找一个节点: 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

查找一个节点的索引: 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

插入一个节点: 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

清空链表: clear()

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

以上就是链表类的要实现的方法。

执行的结果：

接下来是完整代码：

# -*- 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 'error: out of index'
   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 'error: out of index'
   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 = ''
  while node:
   nlist += str(node.data) + ' '
   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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