代写一个自排序的双向链表，实现一个Fruit Store的应用程序。
List Structure
In this project, you are asked to implement a sorted linked list structure to
help a fruit store update its inventory. To simplify this task, we make the
following assumptions:
- The store sells fruits by unit (e.g., an apple, a bunch of grapes, etc.) not by weight.
- Every type of fruit, regardless of its quantity on stock, is displayed in exactly one storage bin.
- Storage bins are numbered consecutively starting at 1, and as many bins as needed are available.
- The names of fruits from the input or passed as arguments to method calls will always be from the list given in Appendix A. (These names are in lower case English letters.)
A doubly-sorted list (DSL) consists of two doubly-linked lists (DLLs), which
share the same set of nodes, and are sorted respectively by two different data
fields. In the DSL, exactly one node N is created for every type of fruit
currently on stock. Shown in the top row of Fig. 1, such a node has three data
fields: fruit, quantity, and bin, which respectively store the name of the
fruit (as a String object), its quantity in units, and the number of its
storage bin. At the bottom of the figure displays two nodes with actual data
values. They record 50 apples stored in bin 5, and 100 bunches of grapes in
bin 8.
In addition to the three data fields, a node N also has two pairs of links:
nextN and previousN, and nextB and previousB. The first pair locates the two
nodes created for the fruits whose names immediately precede and succeed, in
the alphabetical order, the name N.fruit of the fruit represented by N. All
the nextN and previousN links thus form a doubly-linked list (DLL) which
orders the nodes by fruit name. The list, referred to as the N-list, is
accessed via a dummy node headN. Fig. 2 shows an N-list for four different
types of fruits. Note that the last node (“pear”) has its nextN link reference
the dummy node headN.
At the node N, the other two links nextB and previousB respectively reference
the nodes for the fruits stored in the previous and next non-empty bins in the
numerical order. For instance, suppose N references the “apple” node in Fig.
- As the node shows, all apples are displayed in bin 5 at the fruit store.
The last non-empty bin is bin 3, which stores pears, so the link N.previousB
references the “pear” node. Meanwhile, the next non-empty bin is bin 8.
Therefore, N.nextB references the “grape” node. All the nextB and previousB
links induce a second DLL sorted by bin number. It is called the B-list
accessed via a dummy node headB. Fig. 3 displays the B-list formed by the same
four nodes from Fig. 2.
To distinguish between the N- and B-lists, all the nextN and previousN links
will be colored green as in Fig. 2, while all the nextB and previousB links
will be colored blue as in Fig. 3. The DSL is now displayed compactly in Fig.
4 by simply merging the two DLLs from Figs. 2 and 3.
Constructors
There are three constructors:
public DoublySortedList()
public DoublySortedList(String inventoryFile) throws FileNotFoundException
public DoublySortedList(int size, Node headN, Node headB)
—|—
The first one is a default constructor which initializes an empty DSL. Fruits
will be added to the list later using addition methods introduced later. The
second constructor builds a DSL over an inventory file, of which an example is
given below:
pear 40 3
apple 50 5
banana 20 9
grape 100 8
An input inventory file is assumed to always meet the following format
requirements such that there is no need to check for correctness of
formatting:
- Fruits are listed on consecutive lines.
- Each line displays the name of a different fruit, its quantity, and the number of its storage bin, with at least one blank or tab in between.
As in the earlier example, the fruits on an inventory list may not be in the
alphabetical order. In the first stage of construction, you are asked to scan
the list and create a node over every scanned line. The node’s two pairs of
links (nextN, previousN) and (nextB, previousB) are initialized to represent
the order of the scan. The links headN and headB both reference the first
created node. The scan creates two DLLs, neither of which is sorted at the
moment.
In the second stage, an insertion sort is carried out on each DLL by the
following method:
public void insertionSort(boolean sortNList, Comparatorcomp)
—|—
Two comparator classes, NameComparator and BinComparator, are provided for the
insertion sorts by name and by bin number to construct the N- and the B-lists,
respectively. Please note that sorting here is performed on the nodes. You
cannot first put the fruit names or their bins in an array and then sort the
array instead.
The third constructor has been implemented. It will be used for splitting a
DSL into two (to be described in Section 6) and by the TA for testing.
Stocking Fruits
The list is updated whenever new fruits are stocked. Every new fruit type
leads to the creation of a node. For compactness of display, all fruits of
this type should be placed into the first empty bin by number.
Insertion
Addition of a fruit in some specified quantity is carried out by the following
method:
public void add(String fruit, int n) throws IllegalArgumentException
—|—
It starts out with a sequential search in the N-list for fruit. Two possible
situations may arise:
- The search finds a node N housing fruit, simply increase the N.quantity field by n. This is illustrated in Fig. 5 below.
- If no node for fruit is found after the search, the fruit is new on the stock. In this case, a new node is created to store the fruit in the first available bin. To illustrate, suppose that add(“orange”, 70) is executed on the DSL in Fig. 4. A search of the B-list finds the first empty bin to be bin 1. Create the following node (in which the bin number is shown in red).
Next, add the node to the N-list and the B-list by calling two helper methods:
insertN() and insertB(). The first method determines the “orange” node to be
between the “grape” and “pear” nodes, while the second method determines that
it should appear right after headB on the B-list. In Fig. 6, the two links to
be removed are marked with red crosses. Fig. 7 displays the DSL after addition
of the new node (which is now referenced by headB).
You are asked to implement two private methods below to carry out actual
insertions of a node node into the N- and B-lists, respectively.
private void insertN(Node node, Node prev, Node next)
private void insertB(Node node, Node prev, Node next)
—|—
Each method inserts node between two nodes prev and next via updating either
some previousN and nextN links or some previousB and nextB links.
Restocking
Regularly the store is restocked with fruits of multiple types. This is
implemented by the following method:
public void restock(String fruitFile) throws FileNotFoundException, IllegalArgumentException
—|—
The parameter fruitFile is the name of a file which lists fruits line by line,
where each line starts with the fruit name, follows with one or more blanks or
\t, and ends with its quantity. Below is an example file.
pear 40
apple 50
grape 100
banana 20
Selling Fruits
Selling of fruits results in updates of their corresponding nodes. When fruits
of one type are sold out, the node representing the fruit type must be
deleted.
Removal
There are two removal methods, by fruit name and by bin number:
public void remove(String fruit)
public void remove(int bin) throws IllegalArgumentException
—|—
A removal starts by searching either in the N-list with the name fruit or in
the B-list with the number bin. If no matching node is found, simply return.
Otherwise, suppose the matching node is N. Call the following private method
on N to remove it.
private void remove(Node node)
—|—
This method deletes the node from both the N-list and the B-list. An example
of removal by fruit name is shown in Fig. 8. Another example, of removal by
storage bin, is shown in Fig. 9.
Sale
The shop does single sale and bulk sale, which are implemented by the two
methods below:
public void sell(String fruit, int n) throws IllegalArgumentException
public void bulkSell(String fruitFile) throws FileNotFoundException, IllegalArgumentException
—|—
The method sell() first searches the N-list to see if the fruit is on stock.
Nothing needs to be done if the answer is no. Otherwise, a node N is located
for the fruit.
While no check is needed for the correctness of the parameter fruit, an
exception needs to be thrown if the parameter n is less than zero.
The method bulkSell() accepts a file with fruit names and quantities in
exactly the same format accepted by the method restock() (see Section 3.2).
Assumptions e) from Section 2 and g) from Section 3.2 both hold, so there is
no need for file format checking. This method bulkSell() processes an order of
multiple types of fruits in specified quantities. It executes the following
steps:
- Sort the purchased fruits and their quantities by name using the private method quickSort(), in a similar way as described for sorting in implementing restock().
- Simultaneously traverse the N-list and the sorted list of the fruits to be purchased. If the next fruit on the list is not on stock, just ignore its order. Otherwise, a node N with the next purchased fruit will be encountered. Let m be the ordered quantity of this fruit.
Inquiry and Storage Management
Queries for fruit availability can be performed. Every once in a while, the
fruit store checks its inventory. Periodically, it compacts the space by re-
arranging the bins with fruits next to eachother. Occasionally, it needs to
clear all the fruits on stock (due to deterioration of unsold fruits, for
instance).
Inquiry and Output Methods
This category has three methods:
public int inquire(String fruit)
public String printInventoryN()
public String printInventoryB()
—|—
The first method checks the quantity of a fruit on stock. The second method
outputs a string that is printed out to be an inventory listing fruits in the
alphabetical order. Here is sample output of the method from the DSL in Fig.
4.
The following formatting rules apply to the output.
- Entries within each column must be left-aligned.
- The first characters in two adjacent columns are 16 character spaces apart.
You may use the length of a fruit name (which is at most 11 according to the
fruit list in Appendix A). You can make the following assumption:
- The values in the quantity and bin fields will not exceed 3 digits.
The method printInventoryB() outputs a string that is printed out to be an
inventory sorted by the bin number.
Storage Methods
There are two methods to deal with storage bins:
public void compactStorage()
public void clearStorage()
—|—
The first method rearranges the bins containing fruits to be consecutive,
starting at 1, while maintaining their original storage order. To implement
this method, you need only traverse the B-list. See Fig. 12 for an example.
The method clearStorge() clears up the N-list and the B-list by setting the
predecessors and successors of headN and headB to themselves.
