Recursive String Permutations (Practice Interview Question)

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Write a recursive function for generating all permutations of an input string. Return them as a set.

Don't worry about time or space complexity—if we wanted efficiency we'd write an iterative version.

To start, assume every character in the input string is unique.

Your function can have loops—it just needs to also be recursive.

Make sure you have a base case! Otherwise your function may never terminate!

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

It's easy and quick. No "reset password" flow. No password to forget.
It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
It makes it harder for one person to share a paid Interview Cake account with multiple people.

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

It's easy and quick. No "reset password" flow. No password to forget.
It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
It makes it harder for one person to share a paid Interview Cake account with multiple people.

How does the problem change if the string can have duplicate characters?

What if we wanted to bring down the time and/or space costs?

Actually, we don't support password-based login. Never have. Just the OAuth methods above. Why?

It's easy and quick. No "reset password" flow. No password to forget.
It lets us avoid storing passwords that hackers could access and use to try to log into our users' email or bank accounts.
It makes it harder for one person to share a paid Interview Cake account with multiple people.