A function plus a failing test: input, expected, actual. Locate the bug before you look at the answer.
You get the function, the input, what it should return, and what it actually returns. The gap between expected and actual is the whole clue. Bugs are the classic ones interviewers reach for. Cards are drawn with spaced repetition, so the ones you miss come back sooner and the ones you know back off. Progress is kept in your browser.