Question

I would like to create set of strings and below is the only limitation.
Same digit should not repeat.

string Range 1-8(12345678) or 1-16(12345678910111213141516)
For example:(set of series)

12345678
12345687
12345876
12345867
...
...
87654321

Like that 2^8(1-8) and 2^16(1-16) possibilities are there.
How can i generate these strings very efficiently with less computation?

Answer 1

Your 8 case is possible but you will quickly run out of space after that.

This is not a 2^n case like you think it is — it’s an n! case.

For 8, there will be 40,320 permutations.

permute(k,n) = k! / (n-k)!
permute(8,8) = 8! / (8-8)! = 8! = 40320

For 16, there will be 20,922,789,888,000 permutations. At 16 bytes / permutation, you’ll need about 304TB to store them.

@kol’s answer should do the permutations for you but I think you need to change your requirements.