Plaid Software Engineer Interview Experience — Two-Hour Screen Ends on a Syntax Error

I saw online that the first round is usually one hour, but I applied for a backend role and they required two hours back to back, with a 15-30 minute break in the middle.

The first hour's question was a common pipeline question from the forum, and it went smoothly. After I finished, the interviewer was very insistent about how to test it, including wanting asserts in Python rather than print statements.

The pipeline question was roughly: given an input list of tasks, [task_time, num_of_tasks], how long would it take to finish all the tasks. Other posts on the forum go into more detail.

The second hour's question I hadn't seen on the forum before:

Basically the input has several evaluations, and each evaluation can connect to the next evaluation or to true/false. For example:

E1 -> E2
E2 -> true
E5 -> false

Then you need to check whether all the evaluations are valid (for example, a cycle is not valid), and what the final result is, true or false. There can also be multiple evaluation chains — in this example E5 is on its own, while E1 and E2 form one evaluation chain.

In the end I failed... The interviewer watched me get stuck debugging for over ten minutes without saying anything, and it turned out to be a syntax error...