I've written some code (below) which iterates over each character of a string and adds that character to every index of previous permutations.

I have written some code (below) which iterates over each character of a string and adds that character to every index of previous permutations.

Please review code and how it could be improved while keeping it iterative. I am particularly looking for improvements to my existing code, rather than alternative solutions(if possible), so that I can better understand the optimisation process.

Please review code and how it could be improved while keeping it iterative. I am particularly looking for improvements to my existing code, rather than alternative solutions(if possible), so that I can better understand the optimization process.