how do i stop duplicate characters brute force

[cpt pewpew]

Thank you, i have tried it and got it to work

Now to take it to the next level, is there any way that can be used to stop the use of the same letter more than once?

I did read about sed and that would solve this problem but i was wondering if there is a more efficient way from what i read it will take the speed down quite alot

So to stop this
AABCDEAAGHIJCZY
123456373982

But this would work
ABCDEFGHIJKZY
BCDAHFGIHKJYZ
etc

EDIT:
The reason i ask is because from a bruteforce point of view surely it would be easier to start from the bottom with the most simple combinations and work your way up

Instead of jumping straight in the deep end with every combination and a huge waiting/processing time plus you might save a couple of quid in electricity