When the question is clear, we then produce concrete inputs and outputs. These inputs guide a solution for the remainder of the interview so write them on the board!

You may still be unclear how to solve the problem in code, but it’s certain that given an input, X, your function will produce an output, Y.

Make one input the happy path: input that reflects a common scenario.

For example, you’re asked to write a function which capitalizes the first letter of an input string.

A good input could be "apple", which returns "Apple" because this demonstrates the function’s purpose.

If the input were "Apple", it would return "Apple". That’s correct but less informative.

Also think about edge cases, or inputs which do not reflect a common scenario and may cause problems.

For the capitalization function, what should you return if given None as input? Or a number?