## Lecture 7: Hashing, Hash Functions

author: Charles E. Leiserson, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, MIT
recorded by: Massachusetts Institute of Technology, MIT
published: Feb. 10, 2009,   recorded: October 2005,   views: 43111
released under terms of: Creative Commons Attribution Non-Commercial Share Alike (CC-BY-NC-SA)

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# Description

"Today starts a two-lecture sequence on the topic of hashing, which is a really great technique that shows up in a lot of places. So we're going to introduce it through a problem that comes up often in compilers called the symbol table problem. And the idea is that we have a table S holding n records where each record, just to be a little more explicit here. So each record typically has a bunch of, this is record x. x is usually a pointer to the actual data. So when we talk about the record x, what it usually means some pointer to the data. And in the data, in the record, so this is a record, there is a key called a key of x..."

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3 Val Kotlarov, March 31, 2011 at 12:37 a.m.:

Here's the lecturer gives some basic understanding on how the hashing functions work, and analyzes their limitations. Generally he shows how hashing functions map hash keys onto some addressing space where's the values are stored. There's an analysis of the implications. More optimal algorithms is given in the end. The lecture gives you some taste of how the hashmap's size is related to the stored data structure size and what happens if the hashmap gets filled, and in some degree how it affects the algorithm's performance.