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

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Assignment 2 A Simple Address Book

• Andy Wang
• Data Structures, Algorithms, and Generic
  Programming

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Learning Objectives

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

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Mission

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

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Deliverables (Due 9/26/2003)

• makefile
• hashtable.h
• hashtable.cpp
• main.cpp
• Development logs

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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

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Requirements

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

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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)

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Constructor

• Hashtable(unsigned int size)
• Default size 5

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Insert()

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

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Insert()
Name Michael Jackson
Address
0
1
2
3
Hash Table
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Insert()
Name Michael Jackson
Address Never-Never Land
0
1
2
3
Hash Table
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Insert()
Name Michael Jackson
Address Never-Never Land
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
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Insert()
Name Mickey Mouse
Address Disneyland
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
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Insert()
Name Mickey Mouse
Address Disneyland
0
1 Michael Jackson Never-Never Land
2
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Oh, Boy!
Hash Table
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One problem with hashingcollision

• Collision handling techniques
• Increase the hash table size
• Chaining
• Linear probing
• Quadratic probing
• Double hashing

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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!

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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

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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

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Quadratic Probing

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

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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

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Lookup()

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

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Lookup()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
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Lookup()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
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Remove()

• string Remove(const string name) const
• Return value
• The address associated with the name

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Remove()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
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Remove()
Name Michael Jackson
0
1 Michael Jackson Never-Never Land
2
3
Hash Table
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Remove()
Name Michael Jackson
0
1
2
3
Hash Table
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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

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Milestones

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

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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

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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

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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

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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

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Milestones

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

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Pace Yourself

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