I knew the arithmetic series formula but blanked on whether to apply it directly or just loop.
Clarify the incremental pricing rule: for each item, the price per unit decreases by the decrement for each subsequent unit, but never below the floor. Compute the total for each item by summing the prices of all units, then add the flat shipping cost to get the order total.
Pro tip: Discuss edge cases such as when the floor is not provided, when the decrement causes the price to drop below zero, and how to handle large quantities efficiently. Also, mention the importance of using precise decimal arithmetic to avoid floating-point errors in pricing.
Confirm that the price for the first unit is the base price, and each subsequent unit's price is reduced by the decrement, but never below the floor if specified.
For each item, calculate the sum of prices for all units. This can be done by iterating through units or using arithmetic series formulas when possible.
Consider cases where the floor is absent (no lower bound), where the decrement is zero, or where the quantity is zero. Ensure the computation handles these gracefully.
Add up the totals from all items and then add the flat shipping cost to obtain the final order total.
If quantities are large, use closed-form formulas to avoid loops. Verify with a small example to ensure correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.