Python 双向链表的头插尾插

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):    """双向链表节点"""    def __init__(self, item):        self.item = item        self.next = None        self.prev = Noneclass 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

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

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

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()