For this and the next problem, consider the following definition of a circular, doubly-linked list with a sentinel head, in which we have defined a set_cursor method, which sets the cursor attribute to a specified index in the linked list where subsequent operations can be performed.

class LinkedList:

def set_cursor(self, idx):

assert(idx < len(self))

self.cursor = self.head.next

for _ in range(idx):

self.cursor = self.cursor.next

def cursor_insert(self, val):

n = LinkedList.Node(val, prior=self.cursor.prior, next=self.cursor)

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self.length += 1

def cursor_delete(self):

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self.cursor = self.cursor.next

self.length -= 1

cursor_insert should insert the given value val at the current cursor position, and cursor_delete should delete the value at the current cursor position. In both cases, the cursor should refer to the same index as it did before the operation (except in the case of deletion of the last node, which will invalidate the cursor).

Which correctly completes the implementation of cursor_insert?

(a) self.cursor.prior.next = self.cursor.next.prior = n

(b) self.cursor = self.cursor.next = self.cursor.prior = n

(c) self.cursor = self.cursor.prior = self.cursor.next.prior = n

(d) self.cursor.next.prior = self.cursor.prior = self.cursor = n

(e) self.cursor.prior.next = self.cursor.prior = self.cursor = n

Which correctly completes the implementation of cursor_delete?

(a) self.cursor.prior = self.cursor.next

self.cursor.next = self.cursor.prior

(b) self.cursor = self.cursor.next

self.cursor.prior = self.cursor

(c) self.cursor.prior.next = self.cursor.next.prior

self.cursor.next.prior = self.cursor.prior.next

(d) self.cursor.prior.next = self.cursor.next

self.cursor.next.prior = self.cursor.prior

(e) self.cursor.next = self.cursor.next.prior

self.cursor.prior = self.cursor.prior.next