hashing string to an int between 0-19

I was wondering how I would hash a string value (ex: "m开发者_Go百科yObjectName") to int values between 0-19 I'm guaranteed to have no more than 20 unique string values.

Thanks

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Do md5 sum, convert to number and do modulo 20. E.g. in PHP:

hexdec(substr(md5("hello"), 1, 8)) % 20

The substr() is needed so that the number can be converted to integer.

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You could use any sort of hashing you like, but in this case, you could do with adding up the ASCII values (or unicode code point, if you like) of the characters, and apply modulo 20 to the result. It will give you a number from 0 to 19.

But this is nog guaranteed to result in a number that uniquely identifies your 20 strings. No hashing algorithm will guarantee that hashing a collection of 20 random strings will result in a unique code for each string..

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Adding my comment as an answer as suggested:

I would suggest that hashing isn't the exact path you should follow here.

One method would be using a dictionary (like the built in data structure in Python) that has a key-value pair of your string and a number from 1-20 (or 0 - 19)

As you read or see each string, you could check to see if a dictionary entry exists, if so, do whatever needs to be done, if not, create a new dictionary entry with the next available number (generated by looking at the number of existing entries in the dictionary).