Python数据结构与算法3-链表2
- 双链表
拥有两个链接，分别指向前驱节点、后继节点。
定义双链表节点
# 定义节点
class Node(object):
def __init__(self, node = None):
self.elem = node
self.prev = None
self.next = None
双链表操作实现:
# 构造双链表
class DoubleLinkedList(object):
def __init__(self, node = None):
self.__head = node
def is_empty(self):
'''链表是否为空'''
return self.__head == None
def length(self):
'''链表长度'''
cur = self.__head
count = 0
while cur != None:
count += 1
cur = cur.next
return count
def travel(self):
'''遍历整个链表'''
cur = self.__head
while cur != None:
print(cur.elem, end = " ")
cur = cur.next
print("")
def add(self, item):
'''链表头部添加元素，头插法'''
node = Node(item)
# 先将新节点后继链接指向原首节点,原首节点前驱链接指向新节点
node.next = self.__head
node.next.prev = node
# 再讲头指针指向新节点
self.__head = node
def append(self, item):
'''链表尾部添加元素, 尾插法'''
node = Node(item)
if self.is_empty():
self.__head = node
else:
cur = self.__head
while cur.next != None:
# 移动到最后一个节点处
cur = cur.next
# 连接新节点到末尾
cur.next = node
node.prev = cur
def insert(self, pos, item):
'''指定位置添加元素'''
if pos <= 0:
# 当pos<=0时，认为是在头部添加.
self.add(item)
elif pos > self.length()-1:
# 当pos大于总长度时，认为是在尾部添加
self.append(item)
else:
node = Node(item)
cur = self.__head
count = 0
#指针移动到插入位置当前节点处
while count < pos:
count += 1
cur = cur.next
node.next = cur
node.prev = cur.prev
cur.prev.next = node
cur.prev = node
def remove(self, item):
'''删除节点'''
cur = self.__head
while cur != None:
if cur.elem == item:
if cur == self.__head:
# 如果删除元素在头节点,头指针指向头节点后继节点
self.__head = cur.next
if cur.next:
# 判断cur.next是否为空，否则将新的首节点的前驱指针置为空值。
cur.next.prev = None
else:
# 如果在其他位置上，该节点的前驱节点指针直接与该节点的后继节点连接
cur.prev.next = cur.next
if cur.next:
# 判断是否为最后一个元素
cur.next.prev = cur.prev
break
else:
cur = cur.next
def search(self, item):
'''查找节点是否存在'''
cor = self.__head
while cor != None:
if cor.elem == item:
return True
else:
cor = cor.next
return False
-
单项循环链表
与单链表类似，但尾节点指向头节点，而非空值。节点构造与单链表相同。
单项循环链表操作实现：
# 构造单向循环链表
class SingleLinkedList(object):
def __init__(self, node = None):
self.__head = node
if node:
# 若设置起始节点，则起始节点指向自己
node.next = self.__head
def is_empty(self):
'''链表是否为空'''
return self.__head == None
def length(self):
'''链表长度'''
cur = self.__head
if self.is_empty():
# 若链表为空，返回0
return 0
count = 1
while cur.next != self.__head:
count += 1
cur = cur.next
return count
def travel(self):
'''遍历整个链表'''
cur = self.__head
if self.is_empty():
# 若链表为空，返回空值
return
while cur.next != self.__head:
print(cur.elem, end = " ")
cur = cur.next
# 退出循环时，cur停留在尾节点，且未打印。
print(cur.elem)
print("")
def add(self, item):
'''链表头部添加元素，头插法'''
node = Node(item)
if self.is_empty():
self.__head = node
node.next = self.__head
else:
# 找到尾节点
cur = self.__head
while cur.next != self.__head:
cur = cur.next
# 先将新节点指向第一个节点
node.next = self.__head
# 再讲头指针指向新节点
self.__head = node
# 尾节点指向新节点
cur.next = node
def append(self, item):
'''链表尾部添加元素, 尾插法'''
node = Node(item)
if self.is_empty():
self.__head = node
node.next = self.__head
else:
# 找到尾节点
cur = self.__head
while cur.next != self.__head:
cur = cur.next
cur.next = node
node.next = self.__head
def insert(self, pos, item):
'''
指定位置添加元素
与单链表相同
'''
if pos <= 0:
# 当pos<=0时，认为是在头部添加.
self.add(item)
elif pos > self.length()-1:
# 当pos大于总长度时，认为是在尾部添加
self.append(item)
else:
node = Node(item)
pre = self.__head
count = 0
#指针移动到插入位置前一个节点处
while count < pos-1:
count += 1
pre = pre.next
node.next = pre.next
pre.next = node
def remove(self, item):
'''删除节点'''
if self.is_empty():
return
else:
cur = self.__head
pre = None
while cur.next != self.__head:
if cur.elem == item:
if not pre:
# 1.头节点,找到尾节点
rear = self.__head
while rear.next != self.__head:
rear = rear.next
self.__head = cur.next
# 尾节点重新指向新的首节点
rear.next = self.__head
else:
# 2.中间节点，前节点指针直接指向现节点的后继节点
pre.next = cur.next
return
else:
pre = cur
cur = pre.next
if cur.elem == item:
if cur == self.__head:
# 3.链表只有一个元素
self.__head = None
else:
# 4.尾节点
pre.next = self.__head
def search(self, item):
'''查找节点是否存在'''
if self.is_empty():
return False
else:
cur = self.__head
while cur.next != self.__head:
if cur.elem == item:
return True
else:
cur = cur.next
# 判断尾节点
return cur.elem == item