Linear table (doubly linked list (motion picture analysis))

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Although most of the principles in this part are similar to singly linked lists. However, it analyzes "head node, only one node, intermediate node, and tail node" more than singly linked lists, and conducts detailed analysis for more complex operations. The rest of the simple part can refer to "singly linked list".

Doubly linked list

Each node of a doubly linked list or double-sided linked list has two links: one points to the previous node, when this node is the first node, points to a null value; and the other points to the next node, when this node is the last node , Points to a null value.
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Doubly linked list operations

The operation of judging whether the linked list is empty, calculating the length of the linked list, traversing the entire linked list, and finding the specified element is similar to that of a singly linked list

Add elements to the head

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// An highlighted block
"""头部添加元素"""
    def add(self, item):
        node =  DoubleLinkList(item)
        node.next = self._head
        self._head = node
        node.next.prev=node

Add elements at the end

Use the cur cursor to find the tail, and then add new elements
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// An highlighted block
 """尾部添加元素"""
    def append(self, item):
        node = DoubleLinkList(item)
        if self.is_empty():  # 先判断链表是否为空，若是空链表，则将_head指向新节点
            self._head = node  # 若不为空，则找到尾部，将尾节点的next指向新节点
        else:
            cur = self._head
            while cur.next!= None:  # 判断下一个节点是否为None
                cur = cur.next
            cur.next = node
            node.prev=cur

Add element at specified location

Find the position of the element to be added through the cur cursor
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// An highlighted block
"""在指定位置添加元素
    添加的元素是 (2,50)
    """
    def insert(self, pos, item):
        # 判断指定位置是进行头部添加还是尾部添加
        if pos <= 0:
            self.add(item)
        elif pos > (self.length() - 1):
            self.append(item)
        else:
            node = DoubleLinkList(item)
            cur = self._head
            count = 0
            # 通过计数判断是否移动到指定位置
            while count < pos :
                count += 1
                cur = cur.next
            node.next = cur
            node.prev = cur.prev
            cur.prev.next=node
            cur.prev=node

Delete element

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// An highlighted block
   """删除一个节点"""
    def remove(self, item):
        # 若链表为空，则直接返回
        cur = self._head
        # 若头节点的元素就是要查找的元素item
        while cur != None:
            if cur.item == item:
                # 先判断此节点是否为头结点
                if cur == self._head:
                    self._head = cur.next
                    if cur.next:
                        #判断链表中是否只有一个节点
                        cur.next.prev=None
                else:
                    cur.prev.next=cur.next
                    if cur.next:
                        cur.next.prev=cur.prev
                break
            else:
                cur = cur.next

The program runs

// An highlighted block
class DoubleLinkList(object):
    """双链表"""
    def __init__(self,item=None,node=None):
        self.item = item
        self._head = node
        self.next = None

    '''判断链表是否为空'''
    def is_empty(self):
        return self._head == None

    """链表长度"""
    def length(self):
        cur = self._head  # cur初始时指向头节点
        count = 0
        while cur != None:  # 尾节点指向None，当未到达尾部时
            count=count+1
            cur=cur.next  # 将cur后移一个节点
        return count

    """遍历链表"""
    def travel(self):
        cur = self._head
        while cur != None:
            print(cur.item,end="\t")
            cur = cur.next
        print(end="\n")

    """尾部添加元素"""
    def append(self, item):
        node = DoubleLinkList(item)
        if self.is_empty():  # 先判断链表是否为空，若是空链表，则将_head指向新节点
            self._head = node  # 若不为空，则找到尾部，将尾节点的next指向新节点
        else:
            cur = self._head
            while cur.next!= None:  # 判断下一个节点是否为None
                cur = cur.next
            cur.next = node
            node.prev=cur

    """头部添加元素"""
    def add(self, item):
        node =  DoubleLinkList(item)
        node.next = self._head
        self._head = node
        node.next.prev=node

     """在指定位置添加元素  添加的元素是 (2,50)"""
    def insert(self, pos, item):
        # 判断指定位置是进行头部添加还是尾部添加
        if pos <= 0:
            self.add(item)
        elif pos > (self.length() - 1):
            self.append(item)
        else:
            node = DoubleLinkList(item)
            cur = self._head
            count = 0
            # 通过计数判断是否移动到指定位置
            while count < pos :
                count += 1
                cur = cur.next
            node.next = cur
            node.prev = cur.prev
            cur.prev.next=node
            cur.prev=node


    """查找节点是否存在"""
    def search(self, item):
        cur = self._head
        while cur != None:
            if cur.item == item:
                print("True")
                return True
            else:
                cur = cur.next
        print("False")
        return False

    """删除一个节点"""
    def remove(self, item):
        # 若链表为空，则直接返回
        cur = self._head
        # 若头节点的元素就是要查找的元素item
        while cur != None:
            if cur.item == item:
                # 先判断此节点是否为头结点
                if cur == self._head:
                    self._head = cur.next
                    if cur.next:
                        #判断链表中是否只有一个节点
                        cur.next.prev=None
                else:
                    cur.prev.next=cur.next
                    if cur.next:
                        cur.next.prev=cur.prev
                break
            else:
                cur = cur.next



if __name__=="__main__":
    a=DoubleLinkList()
    print(a.is_empty())
    print(a.length())

    #在尾部增加元素
    a.append(1)
    print(a.is_empty())
    print(a.length())
    a.append(10)
    a.append(56)
    a.append(24)
    a.append(78)
    a.append(4)
    a.travel()
    #在头部增加元素
    a.add(20000)
    a.travel()
    # 在指定位置插入
    a.insert(3,50)
    a.travel()
    print(a.length())
    #删除元素
    a.remove(20000)
    a.travel()
    #查找元素
    a.search(50)
    a.search(10000)
    a.search(30000)

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