Lecture16-2

Lecture16-2 - Lecture 16: Hash Tables Motivation Behind...

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Lecture 16: Hash Tables
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Motivation Behind Hash Tables Would like a data structure which allows you to do find, insert, and delete very fast First Attempt: Direct Addressing Suppose the data structure will store integer keys in the range 0 to 99,999 Use an array of size 100,000 Store key k in position k (array positions not containing a key will contain some special value) Can do find, insert, delete in constant time DRAWBACK: Too much wasted space! (if number of keys is much less than size of range)
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Hash Tables Modify previous idea. Idea: Don’t store key k in position k, but in position h(k). h(k) is hash function, takes key as input and produces an index into the array Problem: Collisions! Distinct keys k1 and k2 may have same hash value, i.e. h(k1) = h(k2) Can’t store both k1 and k2 in same array entry
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Different kinds of hash tables Hash table implementations differ in Choice of hash function Method of resolving collisions
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This note was uploaded on 12/09/2009 for the course CS 2134 taught by Professor Hellerstein during the Spring '07 term at NYU Poly.

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Lecture16-2 - Lecture 16: Hash Tables Motivation Behind...

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