双向链表
一种更复杂的链表是“双向链表”或“双面链表”。每个节点有两个链接：一个指向前一个节点，当此节点为第一个节点时，指向空值；而另一个指向下一个节点，当此节点为最后一个节点时，指向空值。
操作
- is_empty() 链表是否为空
- length() 链表长度
- travel() 遍历链表
- add(item) 链表头部添加
- append(item) 链表尾部添加
- insert(pos, item) 指定位置添加
- remove(item) 删除节点
- search(item) 查找节点是否存在
实现
class Node(object):
"""双向链表节点"""
def __init__(self, item):
self.item = item
self.next = None
self.prev = None
class DLinkList(object):
"""双向链表"""
def __init__(self):
self._head = None
def is_empty(self):
"""判断链表是否为空"""
return self._head == None
def length(self):
"""返回链表的长度"""
cur = self._head
count = 0
while cur != None:
count += 1
cur = cur.next
return count
def travel(self):
"""遍历链表"""
cur = self._head
while cur != None:
print cur.item,
cur = cur.next
print ""
def add(self, item):
"""头部插入元素"""
node = Node(item)
if self.is_empty():
# 如果是空链表，将_head指向node
self._head = node
else:
# 将node的next指向_head的头节点
node.next = self._head
# 将_head的头节点的prev指向node
self._head.prev = node
# 将_head 指向node
self._head = node
def append(self, item):
"""尾部插入元素"""
node = Node(item)
if self.is_empty():
# 如果是空链表，将_head指向node
self._head = node
else:
# 移动到链表尾部
cur = self._head
while cur.next != None:
cur = cur.next
# 将尾节点cur的next指向node
cur.next = node
# 将node的prev指向cur
node.prev = cur
def search(self, item):
"""查找元素是否存在"""
cur = self._head
while cur != None:
if cur.item == item:
return True
cur = cur.next
return False
指定位置插入节点
def insert(self, pos, item):
"""在指定位置添加节点"""
if pos <= 0:
self.add(item)
elif pos > (self.length()-1):
self.append(item)
else:
node = Node(item)
cur = self._head
count = 0
# 移动到指定位置的前一个位置
while count < (pos-1):
count += 1
cur = cur.next
# 将node的prev指向cur
node.prev = cur
# 将node的next指向cur的下一个节点
node.next = cur.next
# 将cur的下一个节点的prev指向node
cur.next.prev = node
# 将cur的next指向node
cur.next = node
删除元素
def remove(self, item):
"""删除元素"""
if self.is_empty():
return
else:
cur = self._head
if cur.item == item:
# 如果首节点的元素即是要删除的元素
if cur.next == None:
# 如果链表只有这一个节点
self._head = None
else:
# 将第二个节点的prev设置为None
cur.next.prev = None
# 将_head指向第二个节点
self._head = cur.next
return
while cur != None:
if cur.item == item:
# 将cur的前一个节点的next指向cur的后一个节点
cur.prev.next = cur.next
# 将cur的后一个节点的prev指向cur的前一个节点
cur.next.prev = cur.prev
break
cur = cur.next
测试
if __name__ == "__main__":
ll = DLinkList()
ll.add(1)
ll.add(2)
ll.append(3)
ll.insert(2, 4)
ll.insert(4, 5)
ll.insert(0, 6)
print "length:",ll.length()
ll.travel()
print ll.search(3)
print ll.search(4)
ll.remove(1)
print "length:",ll.length()
ll.travel()
class Node(object):
#节点
def __init__(self,item):
self.item = item
self.prev = None
self.next = None
class DoubleLinkList(object):
#双向链表
def __init__(self,node = None):
self.__head = node
#判空
def is_empty(self):
return self.__head is None
def length(self):
#链表长度
#cur游标，用来移动遍历节点
#len记录数据
len = 0
cur = self.__head
while cur is not None:
len +=1
cur = cur.next
return len
def travel(self):
#遍历
cur = self.__head
while cur != None:
print(cur.item,end =' ')
cur = cur.next
print('')
def add(self,item):
#在链表头部添加元素，头插法
node = Node(item)
node.next = self.__head
self.__head = node
node.next.prev = node
def append(self,item):
#在链表尾部添加元素，尾插法
node = Node(item)
if self.is_empty():
self.__head = node
else:
cur = self.__head
while cur.next is not None:
cur = cur.next
cur.next = node
node.prev = cur
def insert(self,pos,item):
if pos <= 0 :
self.add(item)
elif pos > self.length()-1:
self.append(item)
else:
node = Node(item)
cur = self.__head
for i in range(pos-1):
cur =cur.next
node.prev = cur
node.next = cur.next
cur.next.prve = node
cur.next = node
def remove(self,item):
#删除节点
node = Node(item)
cur = self.__head
while cur != None:
if cur.item == item:
if cur == self.__head:
self.__head = cur.next
if cur.next: #即cur.next is not None,即判断链表是否只有一个节点
cur.next.prev =None
elif cur.next is None:
cur.prev.next = None
else:
cur.prev.next = cur.next
cur.next.prev = cur.prev
break
else:
cur = cur.next
def search(self,item):
cur = self.__head
while cur != None:
if cur.item == item:
return True
else:
cur = cur.next
return False
if __name__ == "__main__":
ll = DoubleLinkList()
print(ll.is_empty())
print(ll.length())
ll.append(1)
print(ll.is_empty())
print(ll.length())
ll.append(2)
ll.add(8)
ll.append(3)
ll.append(4)
ll.append(5)
ll.append(6)
#8 1 2 3 4 5 6
ll.insert(-1,9) #9 8 1 2 3 4 5 6
ll.travel()
ll.insert(3,100)#9 8 1 100 2 3 4 5 6
ll.travel()
ll.insert(10,200) #9 8 1 100 2 3 4 5 6 200
ll.travel()
ll.remove(8)
ll.travel()
ll.remove(200)
ll.travel()
ll.remove(9)
ll.travel()