- A+

This is a question that I was asked in an interview:

Implement a function that gets an integer n and does the following:

1. if n is 3 -> return 7.

2. else if n is 7 -> return 3.

3. otherwise return any number you like (undefined behavior).

Also describe what's the runtime and space complexity of each way.

So first I gave the trivial way of using if-else statement - and said it's `O(1)`

run-time + space complexity. Then the interviewer said: "what if you can't use if statements (including switch-case and other if statements similarities)?"

So I suggested using bitwise operations: `return n^=4`

. Said that it's `O(1)`

run-time + space complexity. Then the interviewer said: "what if you can't use bitwise operations?"

So I suggested using an array like this:

`int mem[8] = {-1, -1, -1, 7, -1, -1, -1, 3}; return mem[n]; `

Said it's `O(1)`

run-time + space complexity, how ever it might be non-efficient if we have large numbers instead of `3`

and `7`

.

Then the interviewer said: "what if you can't use arrays?" - and here I got stuck.

It seems like there is a fourth way... any suggestions?

how about

`def foo(n) return 10 - n end foo(3) => 7 foo(7) => 3 `