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()