Perplexity phone screen, didn't finish the ToDo list problem

Perplexity phone screen, didn't finish the ToDo list problem

Did my Perplexity phone screen for a backend role, wanted to share since I didn't see a ton of detail out there before mine. The problem was the ToDo list for AI, four parts building on classes for Task, TaskStatus, and ToDoList.

Part 1 was straightforward, add, get, update status. Part 2 is where it gets real, dependency tracking. Each task has parent deps and child tasks, and updating a status has to cascade to BLOCKED, READY, or FAILED down the chain. I went with DFS to walk the graph but my solution timed out on one of the larger hidden test cases, guessing there was a cycle or a big fan out I didn't account for.

Ran out of time before part 3 and 4, which seems common from what I've read since. Python is required, no other language option. Got the rejection the next day.

If you get this one, the trap is remembering to track both parents and children, not just one direction. Worth practicing DFS on graph problems under a hard time limit before going in.