How does a hash table work?

Posted by Arec Barrwin on Stack Overflow See other posts from Stack Overflow or by Arec Barrwin
Published on 2009-04-08T15:48:59Z Indexed on 2010/05/15 1:54 UTC
Read the original article Hit count: 377

Filed under:

hashtable

|

hashing

|

data-structures

I'm looking for an explanation of how a hashtable works - in plain English for a simpleton like me! For example I know it takes the key, calculates the hash (how?) and then performs some kind of modulo to work out where it lies in the array that the value is stored, but that's where my knowledge stops.

Could anyone clarify the process.

Edit: I'm not looking specifically about how hashcodes are calculated, but a general overview of how a hashtable works.

© Stack Overflow or respective owner

Related posts about hashtable

Copy hashtable to another hashtable using c++

as seen on Stack Overflow - Search for 'Stack Overflow'
I am starting with c++ and need to know, what should be the approach to copy one hashtable to another hashtable in C++? We can easily do this in java using: HashMap copyOfOriginal=new HashMap(original); But what about C++? How should I go about it? UPDATE Well, I am doing it at a very basic level… >>> More
Search Complexity of a Hashtable within a Hashtable?

as seen on Stack Overflow - Search for 'Stack Overflow'
Say we have a hashtable of size m, and at each bucket we store a hashtable of size p. What would the worst case/average case search complexity be? I am inclined to say that since computing a hash function is still atomic, the only worst case scenario is if the value is at the end of the linked list… >>> More
How to fix the size of the Hashtable and find the whether it has fix size or not?

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi All, I am trying to fix the size of the Hashtable with following code. Hashtable hashtable = new Hashtable(2); //Add elements in the Hashtable hashtable.Add("A", "Vijendra"); hashtable.Add("B", "Singh"); hashtable.Add("C", "Shakya"); hashtable.Add("D"… >>> More
Hi, I have a C hashing routine which is behaving strangely?

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi, In this hashing routine: 1.) I am able to add strings. 2.) I am able to view my added strings. 3.) When i try to add a duplicate string, it throws me an error saying already present. 4.) But, when i try to delete the same string which is already present in hash table, then the lookup_routine… >>> More
Hashtable comparator problem

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi guys i've never written a comparator b4 and im having a real problem. I've created a hashtable. Hashtable <String, Objects> ht; Could someone show how you'd write a comparator for a Hashtable? the examples i've seen overide equals and everything but i simply dont have a clue. The code… >>> More

Related posts about hashing

Is hashing of just "username + password" as safe as salted hashing

as seen on Programmers - Search for 'Programmers'
I want to hash "user + password". EDIT: prehashing "user" would be an improvement, so my question is also for hashing "hash(user) + password". If cross-site same user is a problem then the hashing changed to hashing "hash(serviceName + user) + password" From what I read about salted hash, using… >>> More
Index Hashing vs Normal Hashing

as seen on Stack Overflow - Search for 'Stack Overflow'
What is index hashing ? What are its advantages over regular hashing techniques ? >>> More
Secure hash and salt for PHP passwords

as seen on Stack Overflow - Search for 'Stack Overflow'
It is currently said that MD5 is partially unsafe. Taking this into consideration, I'd like to know which mechanism to use for password protection. Is “double hashing” a password less secure than just hashing it once? Suggests that hashing multiple times may be a good idea. How to implement password… >>> More
SHA512 vs. Blowfish and Bcrypt

as seen on Stack Overflow - Search for 'Stack Overflow'
I'm looking at hashing algorithms, but couldn't find an answer. Bcrypt uses Blowfish Blowfish is better than MD5 Q: but is Blowfish better than SHA512? Thanks.. Update: I want to clarify that I understand the difference between hashing and encryption. What prompted me to ask the question… >>> More
Do encryption algorithms require an internal hashing algorithm?

as seen on Stack Overflow - Search for 'Stack Overflow'
When I use C# to implement the AES symmetric encryption cipher, I noticed: PasswordDeriveBytes derivedPassword = new PasswordDeriveBytes(password, saltBytesArray, hashAlgorithmName, numPasswordIterations); Why do I need to use a hashing algorithm for AES encryption? Aren't they separate? Or is… >>> More