Last to Be Checked
Reported by candidates from Trade Desk's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Trade Desk hit you with 'Last to Be Checked' in March 2024, and it's a queue or simulation problem disguised as a logic puzzle. You've got some kind of ordering or sequencing constraint where the last element matters, and you need to figure out which item or person gets processed last. The OA tests whether you can trace through a system state without overthinking it. StealthCoder is your safety net if the problem statement feels ambiguous in the moment.
Pattern and pitfall
This problem likely involves simulating a process where items move through a queue or get checked off in some order, and you need to identify which one finishes last. The trick is usually recognizing that you don't need to optimize anything, just simulate the system correctly. Common pitfall: candidates build complex state machines when a straightforward queue traversal or single pass works. The pattern is almost certainly simulation or queue-based logic. You read the constraints, trace through the process step by step, and track what's still pending. StealthCoder can feed you the simulation skeleton if you blank on the traversal order.
Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.
You can drill Last to Be Checked cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Made for the candidate who got the OA invite this morning and has 72 hours, not six months.
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Trade Desk reuses patterns across OAs. Made for the candidate who got the OA invite this morning and has 72 hours, not six months. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Last to Be Checked FAQ
Is this a greedy problem or pure simulation?+
Pure simulation. You're not choosing the optimal order, you're figuring out what the last item is given a fixed process. Just walk through the system state and track what remains. No greedy heuristics needed.
How do I know if I need a queue vs. just iterating?+
If items are removed in a FIFO order, use a queue. If you're just marking things as checked in sequence, a simple loop and a set/array works. Read the problem carefully for the processing rule.
What's the most common mistake candidates make?+
Overcomplicating the state. They add priority queues, custom comparators, or recursive logic when the problem just needs you to simulate a straightforward check-off process. Trace one example by hand first.
Can I solve this in 15 minutes if I understand the pattern?+
Yes. Once you know it's simulation, code it like a loop that removes or marks items until one is left. The logic is simple, the gotcha is parsing what 'checked' means in their specific context.
Should I pre-optimize for large inputs?+
Unlikely. Trade Desk's OAs usually aren't trick speed problems at this level. Write clean simulation first. If TLE happens, you can optimize, but the pattern itself is usually O(n) or O(n log n).