python实现双向链表

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。

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):
    def __init__(self):
        self.head = None

    def is_empty(self):
        return self.head is None

    def length(self):
        """返回链表的长度"""
        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.item)
            cur = cur.next
        print("遍历完了")

    def add(self, item):
        node = Node(item)
        if self.is_empty():
            self.head = node
        else:
            node.next = self.head
            self.head.prev = node
            self.head = node

    def append(self, item):
        """尾部插入元素"""
        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 search(self, item):
        cur = self.head
        while cur is not 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
            # 先把node的关系设置好
            node.prev = cur
            node.next = cur.next
            # 再配置cur的关系
            cur.next.prev = node
            cur.next = node

    def remove(self, item):
        """删除元素，元素不存在不报错"""
        if self.is_empty():
            return
        else:
            cur = self.head
            # 如果首节点是要删除的元素
            if cur.item == item:
                if cur.next is 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
                    self.head = cur.next
                return
            # 遍历节点
            while cur is not None:
                if cur.item == item:
                    cur.prev.next = cur.next
                    cur.next.prev = cur.prev
                    break
                cur = cur.next

if __name__ == '__main__':
    lst1 = DLinkList()
    lst1.add(1)
    lst1.add(2)
    lst1.append(3)
    lst1.insert(1, 4)
    lst1.travel()
    print(lst1.is_empty())
    lst1.remove(2)
    lst1.travel()
    lst1.remove(10)
    lst1.travel()

双向链表的实现