I want to build a random and unique strings using 3 random chars from these chars-bank:
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890
How can I calculate the unique (without repetitions) combinations?
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Broshi
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(Number of possible characters)^3 – Jun 03 '16 at 20:48
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@cmorrissey actually its `238328`. OP didn't specify that literals are unique within random string. – lolbas Jun 03 '16 at 20:50
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maybe fun? [Algorithm to return all combinations of k elements from n](http://stackoverflow.com/questions/127704/algorithm-to-return-all-combinations-of-k-elements-from-n) – Ryan Vincent Jun 03 '16 at 21:03
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[combinations and permutations](https://www.mathsisfun.com/combinatorics/combinations-permutations.html) – Barmar Jun 03 '16 at 21:21
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I'm voting to close this question as off-topic because it is about mathematics. – High Performance Mark Jun 04 '16 at 14:54
1 Answers
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- 62^3 = 238,328 with repetitions
- 62 x 61 x 60 = 226,920 without
Pignic
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not sure I understood your answer, and what if I want a length of 4? you just do 62x61x60x59.. ? – Broshi Jun 03 '16 at 20:55
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exactly ! But I don't know why you put a "php" tag on your question, this is more "mathematics" – Pignic Jun 03 '16 at 20:57