The core math is simple enough but I tripped up on the output format at first.
Clarify the billing rules (N free per hour, fixed rate per extra notification) and confirm input/output expectations. Then iterate through the 24 hourly counts, compute each hour's charge as max(0, count - N) * rate, accumulate the total, and return both the total and the array of hourly charges.
Pro tip: Mention edge cases like N=0 (all notifications charged) or counts below N (zero charge), and discuss how to handle potential overflow if counts or rates are large. Also, note that the solution is O(24) time and O(24) space, which is optimal.
Ask about the value of N, the per-notification rate, and whether the rate is constant across hours. Confirm that the input is always an array of 24 non-negative integers and that the output should be a total cost and an array of 24 charges.
For each hour, the charge is max(0, count - N) * rate. Explain that this handles cases where count <= N (charge 0) and count > N (charge for excess).
Loop through the 24 hourly counts, apply the formula to compute each hour's charge, store it in a result array, and add it to a running total.
After the loop, return the total cost and the array of 24 per-hour charges. Ensure the order matches the input hours.
State that the time complexity is O(24) = O(1) and space is O(24) = O(1). Discuss edge cases: N=0, N very large, counts exactly equal to N, and potential integer overflow.
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