PPT-Hash Tables and Sets

Lecture 3 Sets A set is simply a collection of elements Unlike lists elements are not ordered Very abstract general concept with broad usefulness The set of all Google search queries from the past 24 hours. Spencer Dawson. Summary. What are rainbow tables?. A time and memory tradeoff in password cracking.. A piecewise approach to one-way hashes. What are the advantages/disadvantages. Best uses. Limitations. Motivating Applications. Large collection of datasets. Datasets are dynamic (insert, delete). Goal: efficient searching/insertion/deletion. Hashing is ONLY applicable for exact-match searching. Direct Address Tables. Comp 550. Dictionary . Dictionary:. Dynamic-set data structure for . storing items indexed using . keys. .. Supports . operations: Insert, Search, and . Delete . (. take . O. (1) time. ). .. Applications:. Passwords stored in computers are changed from their plain text form to an encrypted value.. These values are called hashes, and there is a unique plain text value for every hash.. A rainbow table is a lookup table offering a time-memory tradeoff used in recovering the plaintext password from a password hash generated by a hash function . . Sections 5.3, 5.4, 5.5, 5.6. 2. Designing a Hash Table. Hash function: establishing a key with an indexed location in a hash table.. E.g. . Index = hash(key) % table_size;. Resolve conflicts: . Need to handle case where multiple keys mapped to the same index.. CIS 606. Spring 2010. Hash tables. Many applications require a dynamic set that supports only the . dictionary . operations . INSERT. , SEARCH, and DELETE. Example: a symbol table in a compiler.. A hash table is effective for implementing a dictionary.. Plan. I spent the last decade advising on numerous cases where hash tables/functions were used. A few observations on . What data structures I’ve seen implemented and where. What do developers think, were they need help. We have:. Discussed techniques for hashing. Discussed mapping down to a given range . 0, ..., . M. – 1. Now we must deal with collisions. Numerous techniques exist. Containers in general. Specifically linked lists. Hash Tables. . . 0. 1. 2. 3. 4. 451-229-0004. 981-101-0002. 025-612-0001. © 2014 Goodrich, Tamassia, Godlwasser. Presentation for use with the textbook . Data Structures and Algorithms in Java, 6. . Outline. Discuss what a hash method does. translates a string key into an integer . Discuss a few strategies for implementing a hash table. linear probing. quadratic probing. separate chaining hashing. 3. Alex Andoni. Plan. 2. Dimension reduction. Application: Numerical Linear Algebra. Sketching. Application: Streaming. Application: Nearest Neighbor Search. and more…. Dimension reduction: . linear . n. . . [from the . techspeak. ] (var. ‘hash clash’) . When used of people, signifies a confusion in associative memory or imagination, especially a persistent one.” . . -. The Hacker's Dictionary . Instructor: Lilian de Greef Quarter: Summer 2017 CSE 373: Data Structures and Algorithms Lecture 6: Finishing Amortized Analysis; Dictionaries ADT; Introduction to Hash Tables Today: Finish up Amortized Analysis CSE 373: Data Structures and Algorithms. Thanks to Kasey Champion, Ben Jones, Adam Blank, Michael Lee, Evan McCarty, Robbie Weber, Whitaker Brand, Zora Fung, Stuart . Reges. , Justin Hsia, Ruth Anderson, and many others for sample slides and materials ....