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8.0

HashTable - Possiblity of Duplicate Hash Values

Asked by Ignyte_Software in Algorithms, Theory, .NET

Tags: hash, hash table, visual basic, .net, .net framework, unique values, hash values

I am working on an application, and I want to use a HashTable to store and lookup data. The key for the HashTable will be a 20-digit bar code.

Everything was going fine until I ran across a couple of articles that says it is possible for more than one text string to result in the same hash value.

*****************

Article 1

The concept of "hashing" in general needs to be clearly understood. A hash (or 'hash value') is a number generated from a string of text. The string could have numbers in it, but for hashing, consider them to be just text characters. The hash value is calculated so that it's unlikely - but not impossible - for some other text string to result in the same hash value. But the calculation guarantees that the same string will always produce the same hash value. Think of the hash as being a nickname for the entire string - a nickname on steroids.

http://visualbasic.about.com/od/usingvbnet/l/aa071203a.htm

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Article 2

A hash function may map two or more keys to the same hash value. In many applications, it is desirable to minimize the occurrence of such collisions; which means that the hash function must map the keys to the hash values as evenly as possible.

http://en.wikipedia.org/wiki/Hash_function

*****************

This concerns me, because I have to be able to pass in a bar code and have the HashTable accurately return the correct data. I cannot have two bar codes creating the same hash value.

Can someone either confirm my fears or put them to rest? What is the likelihood that I could get a duplicate hash value if I load 1 million 20-digit bar codes into a HashTable?

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20091111-EE-VQP-92 - Hierarchy / EE_QW_3_20080625

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1. ozo331,240
2. Infinity08166,433
3. JoseParrot82,306
4. sunnycoder55,988
5. thehagman44,707
6. NovaDeni...36,435
7. jaime_oliv...35,561
8. harfang33,497
9. objects33,379
10. Kdo32,208
11. itsmeandn...31,482
12. CEHJ29,418
13. gregoryyo...26,735
14. d-glitch24,177
15. jkr23,914
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17. sdstuber21,313
18. ikework20,019
19. imladris19,351
20. pepr18,700
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22. evilrix15,367
23. JimBrandley15,188
24. mwvisa115,050
25. angelIII14,818

HashTable - Possiblity of Duplicate Hash Values

Asked by Ignyte_Software in Algorithms, Theory, .NET

Tags: hash, hash table, visual basic, .net, .net framework, unique values, hash values

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