CSCI 340 Computer Assignment 8 Hashing with Linear Probing


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For this computer assignment, you are to write a C++ program to create, search, print,
and manage an item inventory. The program is partially implemented in assignment8.h
and, which are available at
The item inventory information will be kept in a hash table. Each table entry is
described by the following structure, as specified in the header file assignment8.h.
struct Entry {
string key;
string description;
Entry() { key = “—“; }
The key field is the item identifier, which has two uppercase letters followed by a
decimal digit (e.g., AD5 or XR8). The description field contains the item
description. There is a default constructor to create an empty entry, where the key is “–
The item inventory system is defined as a class, named as HT, and its definition is given
in assignment8.h. The hash table hTable (container of type vector < Entry >) is used to store the entries of the item inventory. table_size is the size
of the hash table. item_count records the number of items currently in the system.
The item table can be accessed directly using the linear probing technique to resolve the
collisions. The hash function expects the key of an item as the input argument, and it
returns an integer in the range [ 0 … (table_size−1) ]. The function has the
following prototype: int HT :: hash ( const string& key ). The source
file contains the implementation of this function.
The member functions of HT are described below:
• HT :: HT ( int s=11 ) : This is the constructor. The hash table hTable,
which is a vector of Entry, is created dynamically (with new operator) for a
given size s (with default value 11) here. Other data members are also
properly initialized here.
• HT :: ~HT ( ) : This is the destructor. Since the hash table hTable is
implemented as a dynamically created vector, its memory is released here by
delete operator.
Hashing with Linear Probing
• int HT :: search ( const string& key ) : This public member
function searches the hash table for a record with a given key. It first of all
needs to compute the hash value of the given key. If the search is successful,
this function returns the position of the found item; otherwise, it returns -1.
• bool HT :: insert ( const Entry& e ) : This public member
function inserts item e in the hash table. It first of all checks if the item’s key
already exists in the table or not. If yes, this function prints an error message and
returns false. If the hash table is already full, this function also prints an error
message and returns false. It then needs to compute the hash value of item e’s
key. If the hash table position of the hash value is empty, the item is placed on
that positon; otherwise, an appropriate position is determined by linear probing.
After the item is inserted, item_count is increased and the function returns
• bool HT::remove(const string& s) : This public member function removes
an item with given key s. It first of all searches the given key in the hash table. If
the key is not found, this function simply returns false; otherwise it removes
the entry of the given key by setting its key as “+++”, decreases item_count,
and returns true at the end.
• void HT :: print ( ) : This public member function prints the existing
entries in the hash table: the index value of the position, the key, and the
The input file assignment8input.txt contains operations on the item inventory.
Each line specifies an operation. There are four types of operations, as described below:
• Insertion operation is specified by the format
• Deletion operation is specified by the format
• Search operation is specified by the format
• Print operation is specified by the format
The driver program reads the input file, and conducts proper operations based on the
first character of each line. The main function is completely implemented in You are required to implement two global functions to parse above
Entry* get_entry (const string& line) : This method takes a line of
input and parses it to create a new Entry. The line is in format of A:item-key:itemdescription, i.e., three strings separated by ‘:’, where the first string is just a single
character ‘A’.
string get_key (const string& line) : This method takes a line of input
and parses it to return the item-key. The line is in format of X:item-key, i.e. two
strings separated by ‘:’, where the first string is just a single character.
Programming Note:
• The records stored in the inventory system have unique keys. Duplicate keys are not
• Initially an empty position (a vector element Entry) contains key “—“ (See the
constructor of Entry.) When an entry is deleted at a position, that position then
contains key “+++” (See the remove function of HT.) Both cases indicate a
position is empty and can save a new entry. But for the search operation, you need to
treat two cases differently due to the nature of linear probing technique.
• Include any necessary headers and add necessary global constants.
• You are not allowed to use any I/O functions from the C library, such as scanf or
printf. Instead, use the I/O functions from the C++ library, such as cin or
• In the final version of your assignment, you are not supposed to change existing
code, including class definition and the main method, provided to you in the original
files assignment8.h and You can insert new code to both
files. Usually the source file (.cc) contains the implementation of member methods of
the class(es), together with global functions. You can add inline code in the header
file (.h) when the implementation is very brief, containing just one or two lines for a
member method.
• To compile the source file, execute “ g++ -Wall –o
assignment8.exe”. This will create the executable file assignment8.exe. To
test your program, execute “./assignment8.exe assignment8input.txt &>
assignment8.out”, which will put the output (including any error messages) in
file assignment8.out. You can find the correct output of this program in file
assignment8.out in the directory shown in the last page.
assignment8input.txt is also in that directory.
• Add documentation to your source file.
• Prepare your Makefile so that the TA only needs to invoke the command “make”
to compile your source file and produce the executable file assignment8.exe.
Make sure you use exactly the same file names specified here, i.e.
and assignment8.exe, in your Makefile. Otherwise your submission will get 0
• When your program is ready, submit your files assignment8.h, and Makefile to your TA by following the Assignment
Submission Instructions.