creating a random combination

reldridge

I am creating a random combination(code) for a client. I need to see what the total number of combinations there can be.

Please let me know if I am using the wrong word Combination vs Permutations.

Formula:
2 letters + 2 numbers + 2 letters
example: TR12FR

The random letters are taken from 24 values:
ABCDEFGHJKLMNPQRSTUVWXYZ

The random Numbers are taken from 8 Values:
23456789

Any help would be greatly appreciated.

Thanks
Ryan.

jedishrfu

combination is right you're selecting letters, numbers and more letters:

Choices for each character of your 6 charcter code:

24 * 24 * 8 * 8 * 24 * 24 = total number of codes possible

Now if these could be rearranged then you'd have to worry about permutations to elimnate repeats in your counts.

reldridge

Thank you -

So de-duping these down to create 2.5 million unique codes using this formula will not be an issue, sense there are 21,233,664 possibilities.

jedishrfu

okay what do you mean by de-duping?

reldridge

Well sense this is just a random generator out of excel the possibility of it creating a duplicate is there, so i will need to just remove dupes, or nth select down to 2.5 million unique codes.

Just needed to make sure that the 6 digit using that formula could create that many unique codes.

phinds

So you have a belief that "true" random would not include any dupes?

How would you create 100000 consecutive random numbers from 1 to 100 ?

jedishrfu

this reminds of how new programmers used to construct a deck of randomly sorted cards.

generate a number from 0-51 check if its present in the crd deck array if so then generate another.

The better approach is to generate a sorted sequence of cards into an array and then to randomly shuffle two cards by selecting two indexes at random and swapping the cards.

reldridge

No belief, was just stating that there could be duplicate codes during the random selection and i would need to remove the duplicates until reaching my goal of 2.5 unique codes...

reldridge

Thanks for the help.