Pick the coupon worth most
A customer has several coupons in their wallet and the checkout applies whichever saves them the most on this basket.
- A coupon takes its percentage off, but never more than its cap.
- Choose the coupon with the largest saving.
- If two save the same, take the one whose code sorts first.
- If nothing saves anything, return null.
BestCoupon(basketTotal: int, coupons: list<Coupon>) → string?
C# needs a compiler and Drill does not host one yet, so this page is the reference rather than an exercise: the problem, worked examples, and the solution in full. To type it out, the same problem runs in Python.
Where you start
public string BestCoupon(int basketTotal, List<Coupon> coupons) {
}Worked examples
| Call | Result |
|---|---|
BestCoupon(10000, new List<Coupon> { new Coupon("TEN", 10, 5000), new Coupon("BIG", 50, 2000) }) | "BIG" |
BestCoupon(10000, new List<Coupon> { new Coupon("ZED", 20, 9000), new Coupon("ACE", 20, 9000) }) | "ACE" |
BestCoupon(100, new List<Coupon> { new Coupon("TINY", 0, 500) }) | null |
BestCoupon(10000, new List<Coupon> { }) | null |
Hint
Work out each saving first, then compare. Integer division truncates, which is in the shop’s favour.
Reference solution in C#
public string BestCoupon(int basketTotal, List<Coupon> coupons) {
string bestCode = null;
int bestSave = 0;
foreach (var c in coupons) {
int save = Math.Min((basketTotal * c.PercentOff) / 100, c.MaxOff);
if (save <= 0) continue;
if (save > bestSave || (save == bestSave && bestCode != null && string.CompareOrdinal(c.Code, bestCode) < 0)) {
bestSave = save;
bestCode = c.Code;
}
}
return bestCode;
}