[数据结构与算法] 链表的其他类型
Posted 机器学习和数学
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单链表是最简单的链表，单链表的一种变形就是循环单链表，其中最后一个结点的next域不用None，而是指向表的第一个结点，这样就形成了一种循环结构，所以叫循环单链表。
双链表：单链表只有1个方向的链接，只能做一个方向的扫描和逐步操作。单链表的next指针域指向下一个结点，而双链表结点除了具有next指针外，还有一个previous指针，指向上一个结点。单链表中查找元素只能从头结点开始，根据他的next指针域找到下一个结点，而双链表最大的区别在于不仅能找到下一个结点，还能找到上一个结点。
循环双链表：然后看下什么是循环双链表，循环单链表是把最后一个结点的next指针域指向了首结点，而循环双链表除了这个以外，还有首结点的previous指针域指向尾结点。这就是循环双链表。
下面用Python实现循环单链表和双链表。
Github ： https://github.com/Alvin2580du/Data-Structures-and-Algorithms.git
# - * - coding:utf-8 - * -
"""定义节点类"""
class LNode:
def __init__(self, x, next_=None):
self.elem = x
self.next = next_
"""
定义单链表类
"""
class LList:
def __init__(self):
self._head = None
def length(self):
count = 0 # 数目
# 当前节点
current = self._head
while current != None:
count += 1
# 当前节点往后移
current = current.next
return count
def is_empty(self):
return self._head is None
def prepend(self, elem):
self._head = LNode(elem, self._head)
"""在链表头部添加元素"""
def add(self, elem):
node = LNode(elem)
# 结点的next指针域指向头结点
node.next = self._head
# 头结点称为新的结点
self._head = node
def pop(self):
if self._head is None:
raise ValueError("in pop")
e = self._head.elem
self._head = self._head.next
print("head is :%s" % self._head)
return e
# 后端操作
def append(self, elem):
# 当链表为空时
if self._head is None:
self._head = LNode(elem)
return
current = self._head
while current.next is not None:
current = current.next
current.next = LNode(elem)
def pop_last(self):
if self._head is None:
raise ValueError("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
def find(self, pred):
p = self._head
while p is not None:
if pred(p.elem):
return p.elem
p = p.next
def printall(self):
p = self._head
while p is not None:
if p.next is not None:
print(', ')
p = p.next
"""
定义循环单链表类
"""
class LCList:
def __init__(self):
self._head = None
def is_empty(self):
return self._head is None
# 求链表长度
def length(self):
if self.is_empty():
return 0
count = 1 # 数目
# 当前节点
current = self._head
# 当前节点的下一个节点不是头结点则继续增加
while current.next != self._head:
count += 1
# 当前节点往后移
current = current.next
return count
# add(elem) 链表头部添加元素
def add(self, elem):
node = LNode(elem)
if self.is_empty():
# 空链表
self.__head = node
node.next = node
else:
# 非空链表添加
current = self.__head
# 查找最后一个节点
while current.next != self.__head:
current = current.next
# 新节点的下一个节点为旧链表的头结点
node.next = self.__head
# 新链表的头结点为新节点
self.__head = node
# 最后节点的下一个节点指向新节点
current.next = node
def prepend(self, elem):
p = LNode(elem)
# 如果为空
if self._head is None:
p.next = p
self._head = p
else:
p.next = self._head.next
self._head.next = p
def append(self, elem):
self.prepend(elem)
self._head = self._head.next
def pop(self):
if self._head is None:
raise ValueError("in pop of CLList")
p = self._head.next
if self._head is p:
self._head = None
else:
self._head.next = p.next
return p.elem
# search(elem) 查找节点是否存在
def search(self, elem):
# 当前节点
if self.is_empty():
# 空链表直接返回False
return False
current = self.__head
while current.next != self.__head:
if current.elem == elem:
# 找到了
return True
else:
current = current.next
# 判断最后一个元素
if current.elem == elem:
return True
return False
def printall(self):
if self.is_empty():
return
p = self._head.next
while True:
print (p.elem)
if p is self._head:
break
p = p.next
"""定义双链表结点类，在LNode的基础上派生类"""
class DLNode(LNode):
def __init__(self, elem, prev=None, next_=None):
LNode.__init__(self, elem, next_)
self.prev = prev
"""
定义双链表类
"""
class Double_LList(LList):
def __init__(self):
LList.__init__(self)
def is_empty(self):
return self._head is None
# length() 链表长度
def length(self):
count = 0 # 数目
# 当前节点
current = self._head
while current != None:
count += 1
# 当前节点往后移
current = current.next
return count
# add(elem) 链表头部添加元素
def add(self, elem):
node = DLNode(elem)
# 新节点的下一个节点为旧链表的头结点
node.next = self.__head
# 新链表的头结点为新节点
self.__head = node
# 下一个节点的上一个节点指向新增的节点
# 相当于是第一个结点指向新添加结点
node.next.prev = node
def prepend(self, elem):
p = DLNode(elem, None, self._head)
if self._head is None:
self._head = p
else:
p.prev.prev = p
self._head = p
def append(self, elem):
p = DLNode(elem, self._head, None)
if self._head is None:
self._head = p
else:
p.prev.next = p
self._head = p
def pop(self):
if self._head is None:
raise ValueError("in pop_last of DDList")
e = self._head.elem
self._head = self._head.next
if self._head is not None:
self._head.prev = None
return e
def pop_last(self):
if self._head is None:
raise ValueError("in pop_last of DLList")
e = self._head.elem
self._head = self._head.prev
if self._head is None:
self._head = None
else:
self._head.next = None
return e
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