cs 225
play

CS 225 Data Structures Mar March h 13 13 Ha Hashing Wade Fa - PowerPoint PPT Presentation

CS 225 Data Structures Mar March h 13 13 Ha Hashing Wade Fa Wa Fagen-Ul Ulmsch schnei eider er, , Cra Craig Zi Zilles Has Hashi hing ng Has Hashi hing ng Goals: We want to define a keyspace , a (mathematical)


  1. CS 225 Data Structures Mar March h 13 13 – Ha Hashing Wade Fa Wa Fagen-Ul Ulmsch schnei eider er, , Cra Craig Zi Zilles

  2. Has Hashi hing ng

  3. Has Hashi hing ng Goals: We want to define a keyspace , a (mathematical) description of the keys for a set of data. …use a function to map the keyspace into a small set of integers.

  4. Has Hashi hing ng Hash function …

  5. A Hash Table e based ed Dictionary Client Code: 1 Dictionary<KeyType, ValueType> d; 2 d[k] = v; A Hash Table consists of three things: 1. A hash function, f(k) 2. An array 3. Something to handle chaos when it occurs!

  6. A Per erfec ect Hash Function (Angrave, CS 241) Key Value (Beckman, CS 421) (Cunningham, CS 210) Hash function (Davis, CS 101) (Evans, CS 126) (Fagen-Ulmschneider, CS 225) (Gunter, CS 463) (Herman, CS 233)

  7. A Per erfec ect Hash Function Key Value 0 1 2 3 Keyspace: Rolling 5 dice! 4 5 Hash function 6 7 8 9 10 11 12 13 14 15

  8. Has Hash h Func Functi tion Our hash function consists of two parts: • A hash : • A compression: Choosing a good hash function is tricky… • Don’t create your own (yet*) • Very smart people have created very bad hash functions

  9. Has Hash h Func Functi tion Characteristics of a good hash function: 1. Computation Time: 2. Deterministic: 3. Satisfy the SUHA:

  10. Gen ener eral Purpose e Hash Function Keyspaces … Easy to create if: |KeySpace| N ~

  11. Gen ener eral Purpose e Hash Function Keyspaces … Easy to create if: |KeySpace| N ~ Difficult to Create: …

  12. Gen ener eral Purpose e Hash Function Keyspaces … Easy to create if: |KeySpace| N ~ Difficult to Create: …

  13. MP5 P5

  14. MP5 P5

  15. MP5 P5

Download Presentation
Download Policy: The content available on the website is offered to you 'AS IS' for your personal information and use only. It cannot be commercialized, licensed, or distributed on other websites without prior consent from the author. To download a presentation, simply click this link. If you encounter any difficulties during the download process, it's possible that the publisher has removed the file from their server.

Recommend


More recommend