1 a = 10
2 b = 20
3 a,b = b,a

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# @Date  : 2018-06-12 11:23:21
# @Author : yudanqu (943775910@qq.com)
# @Link  : https://www.cnblogs.com/yudanqu/
# @Version : $Id$


class Node(object):
  """節(jié)點"""

  def __init__(self, elem):
    self.elem = elem
    self.next = None # 初始設(shè)置下一節(jié)點為空

'''
上面定義了一個節(jié)點的類，當(dāng)然也可以直接使用python的一些結(jié)構(gòu)。比如通過元組（elem, None）
'''


# 下面創(chuàng)建單鏈表，并實現(xiàn)其應(yīng)有的功能


class SingleLinkList(object):
  """單鏈表"""

  def __init__(self, node=None): # 使用一個默認(rèn)參數(shù)，在傳入頭結(jié)點時則接收，在沒有傳入時，就默認(rèn)頭結(jié)點為空
    self.__head = node

  def is_empty(self):
    '''鏈表是否為空'''
    return self.__head == None

  def length(self):
    '''鏈表長度'''
    # cur游標(biāo)，用來移動遍歷節(jié)點
    cur = self.__head
    # count記錄數(shù)量
    count = 0
    while cur != None:
      count += 1
      cur = cur.next
    return count

  def travel(self):
    '''遍歷整個列表'''
    cur = self.__head
    while cur != None:
      print(cur.elem, end=' ')
      cur = cur.next
    print("\n")

  def add(self, item):
    '''鏈表頭部添加元素'''
    node = Node(item)
    node.next = self.__head
    self.__head = node

  def append(self, item):
    '''鏈表尾部添加元素'''
    node = Node(item)
    # 由于特殊情況當(dāng)鏈表為空時沒有next，所以在前面要做個判斷
    if self.is_empty():
      self.__head = node
    else:
      cur = self.__head
      while cur.next != None:
        cur = cur.next
      cur.next = node

  def insert(self, pos, item):
    '''指定位置添加元素'''
    if pos <= 0:
        # 如果pos位置在0或者以前，那么都當(dāng)做頭插法來做
      self.add(item)
    elif pos > self.length() - 1:
      # 如果pos位置比原鏈表長，那么都當(dāng)做尾插法來做
      self.append(item)
    else:
      per = self.__head
      count = 0
      while count < pos - 1:
        count += 1
        per = per.next
      # 當(dāng)循環(huán)退出后，pre指向pos-1位置
      node = Node(item)
      node.next = per.next
      per.next = node

  def remove(self, item):
    '''刪除節(jié)點'''
    cur = self.__head
    pre = None
    while cur != None:
      if cur.elem == item:
        # 先判斷該節(jié)點是否是頭結(jié)點
        if cur == self.__head:
          self.__head = cur.next
        else:
          pre.next = cur.next
        break
      else:
        pre = cur
        cur = cur.next

  def search(self, item):
    '''查找節(jié)點是否存在'''
    cur = self.__head
    while not cur:
      if cur.elem == item:
        return True
      else:
        cur = cur.next
    return False


if __name__ == "__main__":

    # node = Node(100) # 先創(chuàng)建一個節(jié)點傳進去

  ll = SingleLinkList()
  print(ll.is_empty())
  print(ll.length())

  ll.append(3)
  ll.add(999)
  ll.insert(-3, 110)
  ll.insert(99, 111)
  print(ll.is_empty())
  print(ll.length())
  ll.travel()
  ll.remove(111)
  ll.travel()