# coding:utf-8
# 双向链表的相关操作：
# 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
class Node(object):
"""节点"""
def __init__(self, item):
self.elem = item
self.prev = None
self.next = None
class DoubleLinkedList(object):
"""双向链表"""
def __init__(self, node=None):
self.__head = node
def is_empty(self):
"""链表是否为空"""
return self.__head is None
def length(self):
"""链表长度"""
cur = self.__head
count = 0
while cur is not None:
count += 1
cur = cur.next
return count
def travel(self):
"""遍历链表"""
cur = self.__head
while cur is not None:
print(cur.elem, end=" ")
cur = cur.next
print("")
def add(self, item):
"""链表头部添加，头插法"""
node = Node(item)
# 注意处理链表为空的情况
if self.is_empty():
self.__head = node
else:
node.next = self.__head
self.__head = node
node.next.prev = node
def append(self, item):
"""链表尾部添加，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当前指向最后一个节点
cur.next = node
node.prev = cur
def insert(self, pos, item):
"""指定位置添加"""
node = Node(item)
# 头插法
if pos <= 0:
self.add(item)
# 尾插法
elif pos > (self.length() - 1):
self.append(item)
# 中间插入
else:
cur = self.__head
count = 0
while count < pos:
count += 1
cur = cur.next
# 循环结束，cur指向要插入的位置
node.next = cur
node.prev = cur.prev
cur.prev.next = node
cur.prev = node
def remove(self, item):
"""删除节点"""
# 先考虑一般情况，再看一般情况下的代码是否适合特殊情况
cur = self.__head
while cur is not None:
if cur.elem == item:
# 判断此节点是否是头节点
if cur == self.__head:
self.__head = cur.next
# 判断链表中是否只有一个节点
if cur.next is not None:
cur.next.prev = None
else:
cur.prev.next = cur.next
# 判断是否是尾节点
if cur.next:
cur.next.prev = cur.prev
break
else:
cur = cur.next
def search(self, item):
"""查找节点是否存在"""
cur = self.__head
while cur is not None:
if cur.elem == item:
return True
else:
cur = cur.next
return False
if __name__ == "__main__":
dll = DoubleLinkedList()
print("before initialized:", dll.is_empty())
print("before initialized:", dll.length())
dll.add(1)
dll.add(2)
dll.add(3)
dll.add(4)
dll.add(5)
dll.add(6)
dll.travel()
dll.append(7)
dll.travel()
dll.insert(3, 100)
dll.travel()
dll.remove(3)
dll.travel()
