Over at Dev102, they are running a weekly series of programming job interview questions. Here is this week’s question:

How would you implement the following method: Foo(7) = 17 and Foo(17) = 7. Any other input to that method is not defined so you can return anything you want. Just follow those rules:

• Conditional statements (if, switch, …) are not allowed.
• Usage of containers (hash tables, arrays, …) are not allowed.

And here is a one-liner that gives the correct answer. There are probably other answers, but this is a simple and fast solution to the problem.

private int Foo(int x)
{
        return (x + 10) % 20;
}