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Creating a random combination

by reldridge
Tags: combination, creating, random
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reldridge
#1
Dec3-12, 02:10 PM
P: 5
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.
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jedishrfu
#2
Dec3-12, 02:18 PM
P: 2,939
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
#3
Dec3-12, 02:22 PM
P: 5
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
#4
Dec3-12, 02:39 PM
P: 2,939
Creating a random combination

okay what do you mean by de-duping?
reldridge
#5
Dec3-12, 02:46 PM
P: 5
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
#6
Dec3-12, 02:51 PM
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P: 6,283
Quote Quote by reldridge View Post
Well sense this is just a random generator out of excel the possibility of it creating a duplicate is there ...
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
#7
Dec3-12, 03:02 PM
P: 2,939
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
#8
Dec3-12, 03:22 PM
P: 5
Quote Quote by phinds View Post
So you have a belief that "true" random would not include any dupes?
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
#9
Dec3-12, 03:23 PM
P: 5
Thanks for the help.


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