雙向鏈表——python

class Node(object):
    "雙向鏈表節點"
    def __init__(self,item):
        self.item=item
        self.next=None  #後
        self.prev=None  #前

class doublelist(object):
    "雙向鏈表"
    def __init__(self):
        self._head=None #頭節點

    # is_empty() 鏈表是否爲空
    def is_empty(self):
        return self._head is None

    # length() 鏈表長度
    def length(self):
        count=0
        cur=self._head
        while cur!=None:
            count+=1
            cur=cur.next
        return count

    #顯示輸出列表
    def printlist(self):
        cur=self._head
        while cur!=None:
            print(cur.item)
            cur=cur.next

    # add(item) 鏈表頭部添加
    def add(self, item):
        node = Node(item)
        # 當鏈表爲空
        if self.is_empty():
            node.next=self._head
            self._head=node
        else:
            node.next = self._head
            self._head.prev = node
            self._head = node

    # append(item) 鏈表尾部添加
    def append(self,item):
        node = Node(item)
        cur=self._head
        if self.is_empty():
            node.next=cur
            self._head=node
        else:
            while cur.next!=None:
                cur=cur.next
            cur.next=node
            node.prev=cur
    # insert(pos, item) 指定位置添加
    def insert(self,pos,item):
        if not isinstance(pos,int):
            raise TypeError
        if pos>self.length():
            print('超出列表長度')
            return
        if pos < 0:
            raise IndexError
        if pos==0:
            "表頭添加"
            self.add(item)
        elif pos == self.length():
            "表尾添加"
            self.append(item)
        else:
            # 否則就是正常情況
            node = Node(item)
            cur = self._head
            count=0
            while count<pos:#插入地方得到前一個節點
                count+=1
                cur=cur.next
            cur.prev.next = node
            node.prev = cur.prev
            node.next = cur
            cur.prev = node

    # remove(item) 刪除節點
    def remove(self,item):
        cur=self._head
        if cur==None:
            print("元素不存在")
            return
        # 當刪除的是第一個元素
        if cur.item == item:
            self._head = cur.next
            return
        while cur.item!=item:
            cur=cur.next
            if cur==None:
                print("元素不存在")
                return
        if cur.next==None:
            cur.prev.next=None
        else:
            cur.prev.next=cur.next
            cur.next.prev=cur.prev

    # search(item) 查找節點是否存在
    def search(self,item):
        cur=self._head
        if cur==None:
            print(False)
            return
        else:
            while cur.item!=item:
                cur=cur.next
                if cur==None:
                    print(False)
                    return
            print(True)
            return
if __name__=="__main__":
    d=doublelist()
    d.insert(0,0)
    d.insert(1,1)
    d.insert(2, 2)
    d.search(0)