Objective: To gain experience using a cursor-based list by implementing a text-editor program. Plus, it provides
experience using a doubly-linked list with header and trailer nodes.
To start the homework: Download and extract the file hw3.zip from
/ /
The hw3.zip file contains:
the Node class (in the node.py module) and the Node2Way class (in the node2way.py module)
the skeleton CursorBasedList class (in the cursor_based_list.py module) which you will complete
the cursorBasedListTester.py file that you can use to interactively test your CursorBasedList class.
Part A: Recall that in a cursor-base list a cursor (indicating the current item) can be moved around the list with
the cursor being used to identify the region in the list to be manipulated. We will insert and removing items
relative to the current item. A current item which is always defined as long as the list is not empty.
Precondition: the list is not empty. Removes and returns the current item.
Making the next item the current item if one exists; otherwise the tail item in
the list is the current item unless the list in now empty.
L.remove()
Precondition: the list is not empty. Replaces the current item by the newValue.
L.replace(newValue)
Inserts item before the current item, or as the only item if the list is empty. The
new item is the current item.
L.insertBefore(item)
Inserts item after the current item, or as the only item if the list is empty. The
new item is the current item.
L.insertAfter(item)
Precondition: the list is not empty. Makes the last item the current item.
L.last()
Precondition: the list is not empty. Makes the first item the current item.
L.first()
Precondition: hasPrevious returns True. Postcondition: The current item has
moved left one item
L.previous()
Precondition: the list is not empty. Returns True if the current item has a
previous item; otherwise return False.
L.hasPrevious()
Precondition: hasNext returns True. Postcondition: The current item has moved
right one item
L.next()
Precondition: the list is not empty. Returns True if the current item has a next
item; otherwise return False.
L.hasNext()
Precondition: the list is not empty. Returns the current item without removing
it or changing the current position.
L.getCurrent()
Description of operationCursor-based operations
The cursor_based_list.py file contains a skeleton CursorBasedList class. You MUST uses a
doubly-linked list implementation with a header node and a trailer node. An empty list looks like:
previous data next previous data next
_header
_current
_trailer
_size 0
All “real” list items will be inserted between the header and trailer nodes to reduce the number of “special cases”
(e.g., inserting first item in an empty list, deleting the last item from the list).
Use the provided cursorBasedListTester.py program to test your list.
Data Structures (CS 1520) Homework #3
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