数据结构笔记：单向循环链表

原文地址

分类目录——数据结构笔记

普通单链表的结尾元素的next=None，循环链表就是将结尾元素的next=head

• 节点实现（同单链表）

  class Node(object):
      def __init__(self, value):
          self.value = value
          self.next = None
  

• 单向循环列表实现及常用方法

  比之单项非循环链表，结尾元素的next指向了head，使其一些方法需要单独考虑对于链表收尾的操作。

  class SinglCycleLinkList(object):
      def __init__(self, node=None):
          self.head = None
          if node:    # 每加入一个节点，就是一个指向自己的循环链表？
              node.next = node
  
      def is_empty(self):
          '''判断链表是否为空'''
          return self.head == None
  
      def length(self):
          '''返回链表长度'''
          if self.is_empty(): # 如果链表为空
              return 0
          cur = self.head  # 指针
          count = 1  # 计数器
          while cur.next != self.head:
              count += 1
              cur = cur.next
          return count
  
      def travel(self):
          '''遍历链表'''
          if self.is_empty():
              return
          cur = self.head  # 指针
          while cur.next != self.head:
              print(cur.value, end=' ')
              cur = cur.next
          print(cur.value)
  
      def add(self, value):
          '''头部插入——头插法'''
          node = Node(value)
          if self.is_empty():
              self.head = node
              node.next = self.head
          else:
              cur = self.head
              while cur.next != self.head:
                  cur = cur.next
              node.next = self.head  # 把新节点夹在head之前
              self.head = node       # 链表的新头部编程node
              cur.next = self.head   # 尾部指向新头部
  
  
      def append(self, value):
          '''尾部插入——尾插法'''
          node = Node(value)
          if self.is_empty():
              self.head = node
              node.next = self.head
          else:
              cur = self.head
              while cur.next != self.head:
                  cur = cur.next
              cur.next = node
              node.next = self.head
  
      def insert(self, index, value):
          '''
          :param index: the position of insert(start from 0)
          :param value: node.value
          :return:
          '''
          node = Node(value)
          if index <= 0:
              self.add(node)
          elif index > self.length():
              self.append(node)
          else:
              cur = self.head
              count = 0
              while count < index - 1:
                  count += 1
                  cur = cur.next
              node.next = cur.next
              cur.next = node
  
      def remove(self, item):
          '''从链表中删除item'''
          # 如果为空
          if self.head == None:
              return
          # 如果第一个命中
          if self.head.value == item:
              # 如果只有一个元素
              if self.length() == 1:
                  self.head = None
                  return
              else:
                  rear = self.head    # 用这个索引去找尾
                  while rear.next != self.head:
                      rear = rear.next
                  self.head = self.head.next
                  rear.next = self.head
          else:
              cur = self.head
              while cur.next != self.head and cur.next.value != item:
                  cur = cur.next
              if cur.next.value == item:
                  cur.next = cur.next.next
  
      def search(self, item):
          '''在链表中查找item，含有返回True，不含返回False（因为是链表，返回索引也没有意义）'''
          if self.is_empty():
              return False
          cur = self.head
          if cur.value == item:
              return True
          else:
              while cur != self.head:
                  cur = cur.next
                  if cur.value == item:
                      return True
              return False