def deleteAtIndex(self,index): if index < 0 or index >= self.size: return if index == 0: self.head = self.head.next if self.head: self.head.prev = None else: self.tail = None elif index == self.size - 1: self.tail = self.tail.prev if self.tail: self.tail.next = None else: self.head = None else: if index < self.size // 2: current = self.head for i in range(index): current = current.next else: current = self.tail for i in range(self.size - index - 1): current = current.prev current.prev.next = current.next current.next.prev = current.prev self.size -= 1 代码解释

这是一个双向链表的删除节点方法。其中，self.head 和 self.tail 分别表示链表的头节点和尾节点，self.size 表示链表的大小。具体解释如下：

1. 如果 index 小于 0 或者大于等于链表的大小，则直接返回，不进行删除操作。

2. 如果要删除的是头节点，将头节点指向下一个节点，并将下一个节点的 prev 指向空。如果链表只有一个节点，将尾节点也置空。

3. 如果要删除的是尾节点，将尾节点指向前一个节点，并将前一个节点的 next 指向空。如果链表只有一个节点，将头节点也置空。

4. 如果要删除的是中间节点，先计算当前节点是在链表的前半段还是后半段，从而选择从头节点还是尾节点开始遍历，直到找到要删除的节点。将该节点的 prev 的 next 指向该节点的 next，将该节点的 next 的 prev 指向该节点的 prev。

5. 最后将链表的大小减一。

相关问题

def addAtIndex(self,index,val): if index < 0 or index > self.size: return -1 if index == self.size: self.addAtTail(val) return current = self.head for i in range(index-1): current = current.next new_node = Listnode(val,current,current.next) current.next.prev = new_node current.next = new_node self.size += 1 AttributeError: 'NoneType' object has no attribute 'prev' current.next.prev = new_node 请修改

这段代码中可能存在两个问题：

1. 如果链表为空，即 self.head 为 None，那么在第 9 行的 for 循环中会报错。因此需要在第 3 行加上判断链表是否为空的条件。

2. 如果插入的位置是最后一个结点，即 index == self.size，那么在第 7 行调用 addAtTail 方法后，函数应该返回而不是继续执行。因此需要在第 8 行加上 return 语句。

修改后的代码如下：

def addAtIndex(self, index, val):
    if index < 0 or index > self.size:
        return -1
    if index == self.size:
        self.addAtTail(val)
        return
    if self.head is None:
        self.addAtHead(val)
        return
    current = self.head
    for i in range(index-1):
        current = current.next
    new_node = ListNode(val, current, current.next)
    current.next.prev = new_node
    current.next = new_node
    self.size += 1

这样就可以避免空指针异常和插入最后一个结点时的错误。

约瑟夫环改错class Node: def __init__(self,data): self.data=data self.next=Noneclass linklist: def __init__(self): self.head=None self.data=None def isEmpty(self): if self.head: return False else: return True def length(self): if self.isEmpty(): return 0 else: t = self.head n = 1 while t.next: if t.next == self.head: break t = t.next n = n + 1 return n def addhead(self,data): node = Node(data) if self.isEmpty(): self.head = node self.tail = self.head else: node.next = self.head self.head = node self.tail.next = self.head def addtail(self,data): node=Node(data) if self.isEmpty(): self.addhead(data) else: t=self.head n=1 l=self.length() while n<l: n=n+1 t=t.next t.next=node node.next=self.head self.tail=node def delete(self,index): if self.isEmpty(): print("The linked list is empty") else: t = self.head l = self.length() if index == 0: self.head = t.next self.tail.next = self.head elif index == l - 1: n = 1 while n < l - 1: t = t.next n = n + 1 t.next = self.head self.tail = t elif index > l - 1: print("Out of range") elif index < 0: print("Wrong operation") else: n = 1 while n < index - 1: t = t.next n = n + 1 a = t.next.next t.next = a def insert(self,data,index): l = self.length() if index == 0 or self.isEmpty(): self.addhead(data) elif index >= l: self.addtail(data) else: node = Node(data) t = self.head n = 1 while n < index - 1: t = t.next n = n + 1 a = t.next t.next = node node.next = a def search(self,a): t=self.head for i in range(a): t=t.next return t.data def form(self,datalist): self.addhead(datalist[0]) for i in range(1,len(datalist)): self.addtail(datalist[i]) t = self.head while t.next != self.head: t = t.nextn,p=map(int,input().split(' '))data=[]p=p-1for i in range(1,n+1): data.append(i)print(data)datalist=[]for i in range(len(data)): datalist.append(int(data[i]))link=linklist()link.form(datalist)a=pb=[]while link.length()>0: b.append(link.search(a)) link.delete(a) a=a+p while a>=link.length(): a=a-link.length()print(b)

改错如下：

class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class LinkList:
    def __init__(self):
        self.head = None
        self.tail = None
    
    def isEmpty(self):
        if self.head:
            return False
        else:
            return True
    
    def length(self):
        if self.isEmpty():
            return 0
        else:
            t = self.head
            n = 1
            while t.next:
                if t.next == self.head:
                    break
                t = t.next
                n += 1
            return n
    
    def addhead(self, data):
        node = Node(data)
        if self.isEmpty():
            self.head = node
            self.tail = self.head
        else:
            node.next = self.head
            self.head = node
            self.tail.next = self.head
    
    def addtail(self, data):
        node = Node(data)
        if self.isEmpty():
            self.addhead(data)
        else:
            t = self.head
            n = 1
            l = self.length()
            while n < l:
                n += 1
                t = t.next
            t.next = node
            node.next = self.head
            self.tail = node
    
    def delete(self, index):
        if self.isEmpty():
            print("The linked list is empty")
        else:
            t = self.head
            l = self.length()
            if index == 0:
                self.head = t.next
                self.tail.next = self.head
            elif index == l - 1:
                n = 1
                while n < l - 1:
                    t = t.next
                    n += 1
                t.next = self.head
                self.tail = t
            elif index > l - 1:
                print("Out of range")
            elif index < 0:
                print("Wrong operation")
            else:
                n = 1
                while n < index:
                    t = t.next
                    n += 1
                a = t.next.next
                t.next = a
    
    def insert(self, data, index):
        l = self.length()
        if index == 0 or self.isEmpty():
            self.addhead(data)
        elif index >= l:
            self.addtail(data)
        else:
            node = Node(data)
            t = self.head
            n = 1
            while n < index:
                t = t.next
                n += 1
            a = t.next
            t.next = node
            node.next = a
    
    def search(self, a):
        t = self.head
        for i in range(a):
            t = t.next
        return t.data
    
    def form(self, datalist):
        self.addhead(datalist[0])
        for i in range(1, len(datalist)):
            self.addtail(datalist[i])
        t = self.head
        while t.next != self.head:
            t = t.next

n, p = map(int, input().split(' '))
data = [i for i in range(1, n+1)]
print(data)

datalist = []
for i in range(len(data)):
    datalist.append(data[i])

link = LinkList()
link.form(datalist)

a = p-1
b = []
while link.length() > 0:
    b.append(link.search(a))
    link.delete(a)
    a += p-1
    while a >= link.length():
        a -= link.length()

print(b)