我怎样才能将字符串散列到特定数量的桶中

Question

I'm trying to come up with an algorithm to hash a string into a specific number of buckets but haven't had any luck coming up with ideas on how to do this?

I have a list of strings like this:

a.jpg
b.htm
c.gif
d.jpg
e.swf

and i would like to run a function to get a number between 1 and 4 based on the string.

egajpg would be 3
b.htm would be 2
c.gif would be 1
etc

it needs to be consistent so if i run the function on a.jpg it always returns 3.

this algorithm would be for splitting resources between servers...

egajpg would be accessed from server3.mydomain.com
b.htm would be accessed from server2.mydomain.com
etc

Does anyone know how I would go about doing this?

Any advice would be much appreciated!

Cheers

Tim

Answer 1

You may find the following blog post useful. The proposed algorithm is:

int bucketIndex = (int)((uint)"d.jpg".GetHashCode() % (uint)buckets.Length);

Answer 2

int bucket = (int)(unchecked(((uint)s.GetHashCode())) % 4 + 1)

（其中s是字符串）

Answer 3

Standard GetHashCode and % will work: Math.Abs("aaaa".GetHashCode()) % numberOfBuckets .

EDIT thanks Thomas Levesque for reminding of GetHashCode() returning < 0. Added Math.Abs to have correct code, but versions in other answers are likely work better.

Answer 4

Use a hash algorithm based on a shared machine key. This will create a unique identifier per string. If you require integers then use a dictionary object to map strings to ints. Every time you add a new string set its key to the current dictionary length. Finally store the dictionary in a farm based state object such as a shared session so that each site instance can reference it.