Count Signals
Reported by candidates from JP Morgan's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
JP Morgan's August 2024 OA included a signal-counting problem that caught candidates off guard. You're looking at a problem that sounds simple on the surface but requires you to recognize when a pattern repeats or when a condition triggers. The trick isn't math-heavy; it's about reading the problem carefully and avoiding off-by-one errors. If you blank on the exact algorithm during the live assessment, StealthCoder runs invisibly and reads the problem, giving you the pattern in real time so you can code with confidence.
Pattern and pitfall
Signal counting problems typically involve iterating through data and tallying occurrences where a specific condition is met. The gotcha is usually in how you define 'signal', is it a transition, a threshold crossing, a consecutive sequence, or a state change. Most candidates rush and miscount by including or excluding boundary cases. The pattern usually falls under simulation or counting, depending on whether you're tracking state changes or just incrementing a counter. During the live OA, if the problem statement is ambiguous, StealthCoder lets you see the exact wording again, reparse it, and implement the correct logic without time pressure or panic. The typical solution is O(n) pass with a single counter or state machine.
Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.
You can drill Count Signals 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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JP Morgan 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.
Count Signals FAQ
Is this a math problem or a simulation?+
It's simulation. You're reading through data and counting events. No formulas. The trick is defining what counts as a 'signal' correctly. Re-read the problem statement once more before coding.
What's the common mistake candidates make?+
Off-by-one errors and misinterpreting what 'signal' means. Some count the first occurrence, others skip it. Some count transitions, others count states. Trace through the example by hand first.
How do I prepare in 24 hours?+
Don't study counting problems in general. Instead, practice reading ambiguous problem statements carefully and asking clarifying questions mentally. Trace examples on paper. Speed comes after clarity.
Is this problem still being asked at JP Morgan?+
It was reported in August 2024. Signal-counting variants are a staple in finance and trading interviews. Expect similar logic on your OA.
What if I freeze during the OA?+
That's why StealthCoder exists. It reads the problem silently on your screen and gives you the approach. You won't be stuck staring at ambiguous wording.