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Assignment%202:%20%20A%20Simple%20Address%20Book

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Data Structures ... project develop using make Apply the concept of hash functions Mission Write a simple address ... entries before size increase Clustering ... – PowerPoint PPT presentation

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Title: Assignment%202:%20%20A%20Simple%20Address%20Book


1
Assignment 2 A Simple Address Book
  • Andy Wang
  • Data Structures, Algorithms, and Generic
    Programming

2
Learning Objectives
  • Gain further experience in C
  • Manage project develop using make
  • Apply the concept of hash functions

3
Mission
  • Write a simple address book
  • Use hash functions to access a table
  • Insertion
  • Lookup
  • Deletion

4
Deliverables (Due 9/26/2003)
  • makefile
  • hashtable.h
  • hashtable.cpp
  • main.cpp
  • Development logs

5
More on Development Log
  • Due in each class
  • Cumulative
  • 9/17, turn in a log that covers 9/15 9/17
  • 9/22, turn in a log that covers 9/15 9/22
  • And so on

6
Requirements
  • Create a proj2 directory
  • makefile
  • hashtable.h
  • hashtable.cpp
  • main.cpp

7
hashtable.h
  • Interface of the class HashTable
  • Required public interface
  • bool Insert(const string name, const string
    addr)
  • bool Lookup(const string name, string addr)
    const
  • string Remove(const string name)

8
Constructor
  • Hashtable(unsigned int size)
  • Default size 5

9
Insert()
  • bool Insert(const string name, const string
    addr)
  • Return value
  • true on success
  • false on failure
  • Duplicate name
  • Table is full

10
Insert()
Name Michael Jackson
Address
0
1
2
3
Hash Table
11
Insert()
Name Michael Jackson
Address Never-Never Land
0
1
2
3
Hash Table
12
Insert()
Name Michael Jackson
Address Never-Never Land
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
13
Insert()
Name Mickey Mouse
Address Disneyland
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
14
Insert()
Name Mickey Mouse
Address Disneyland
0
1 Michael Jackson Never-Never Land
2
3
Oh, Boy!
Hash Table
15
One problem with hashingcollision
  • Collision handling techniques
  • Increase the hash table size
  • Chaining
  • Linear probing
  • Quadratic probing
  • Double hashing

16
Increase the Hash Table Size
  • If collision, double the size, rehash all entries
    Conceptually simple
  • Unbounded growth of table size
  • Birthday Paradox
  • In a group of 60 people, you are very likely to
    find two people with the same birthday.
  • The probability of collisions is higher than you
    think!

17
Chaining
  • Requires a data structure from a later lecture
  • Basic idea each table entry is associated with
    multiple (key, value) pairs
  • Sequentially look through those pairs
  • incremental growth of the table
  • - poor performance when an entry is associated
    with too many (key, value) pairs

18
Linear Probing
  • Sequentially find the next empty table entry
  • (Hash(key) 1) size
  • (Hash(key) 2) size
  • Simple
  • Use all table entries before size increase
  • Clustering (nonuniform distribution of table
    entries)
  • Can degenerate into sequential searches

19
Quadratic Probing
  • Try to avoid clustering
  • (Hash(key) 12) size
  • (Hash(key) 22) size
  • Simple
  • - Secondary clustering (not as severe)

20
Double Hashing
  • Use another hash function to determine the
    skipping distance
  • If Hash1(key) points to an occupied entry
  • Use (Hash1(key) Hash2(Hash1(key))) size
  • (Hash1(key) 2Hash2(Hash1(key)) size
  • Avoids secondary clustering
  • Widely used in compilers

21
Lookup()
  • bool Lookup(const string name, string address)
    const
  • Return value
  • true if found
  • address contains the address
  • false if not found

22
Lookup()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
23
Lookup()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
24
Remove()
  • string Remove(const string name) const
  • Return value
  • The address associated with the name

25
Remove()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
26
Remove()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
27
Remove()
Name Michael Jackson
0
1
2
3
Hash Table
28
Your Hash Function
  • Hash(name) // may contain spaces
  • Develop/choose your own hash function(s)
  • Use all characters in the name
  • Use the ordering information of each character
  • Short names should not cluster in the table

29
Milestones
  • 1. Create all files
  • Add include into .cpp files
  • Add ifndef into .h files
  • Add files names into the makefile
  • make clean
  • make

30
Milestones
  • 2. Add the class definitions to the header files
  • Try to compile
  • 3. Write the skeleton code in your .cpp files
  • Nothing but empty functions
  • Try to get the interface to compile
  • 4. Write pseudo code (comments) in each skeleton
    function

31
Milestones
  • 5. Implement the constructor/destructor routines
  • Add private functions as needed
  • Compile and test those routines
  • 6. Implement a dump routine to visualize the hash
    table

32
Milestones
  • 7. Implement the accessor routines that only read
    your private data members
  • Compile and test those routines
  • 8. Implement the accessor routines that write to
    your private data members
  • Compile and test those routines

33
Milestones
  • 9. Implement the Insert routine
  • Implement the associated hash function(s)
  • Test the hash function in isolation
  • Check for clustering
  • Check for duplicate names
  • 10. Implement collision handling

34
Milestones
  • 11. Implement the Lookup routine
  • Compile and test the routine
  • 12. Implement the Remove routine. Compile and
    test the routine

35
Pace Yourself
  • Try to accomplish 1 to 2 milestones per day
  • Start your project early!
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