lec5 - MIT OpenCourseWare http:/ocw.mit.edu 6.006...

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MIT OpenCourseWare http://ocw.mit.edu 6.006 Introduction to Algorithms Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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5 Hashing I: Chaining, Hash Functions 6.006 Spring 2008 Lecture 5: Hashing I: Chaining, Hash Functions Lecture Overview Dictionaries and Python Motivation Hash functions Chaining Simple uniform hashing “Good” hash functions Readings CLRS Chapter 11. 1, 11. 2, 11. 3. Dictionary Problem Abstract Data Type (ADT) maintains a set of items, each with a key, subject to insert(item): add item to set delete(item): remove item from set search(key): return item with key if it exists assume items have distinct keys (or that inserting new one clobbers old) balanced BSTs solve in O (lg n ) time per op. (in addition to inexact searches like nextlargest). goal: O (1) time per operation. Python Dictionaries: Items are (key, value) pairs e.g. d = ‘algorithms’: 5, ‘cool’: 42 d.items() [(‘algorithms’, 5),(‘cool’,5)] d[‘cool’] 42 d[42] KeyError ‘cool’ in d True 42 in d False Python set is really dict where items are keys. 1
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This note was uploaded on 09/24/2010 for the course CS 6.006 taught by Professor Erikdemaine during the Spring '08 term at MIT.

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lec5 - MIT OpenCourseWare http:/ocw.mit.edu 6.006...

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