Apply credits to an invoice
Customer credits are applied against an invoice in order. Return the remaining unpaid balance.
- Apply credits in list order, each subtracting from the running balance.
- The balance is clamped at 0 — credits never produce a negative result.
creditFirst(invoiceTotal: int, credits: list<Credit>) → int
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
int creditFirst(int invoiceTotal, std::vector<Credit> credits) {
}Worked examples
| Call | Result |
|---|---|
creditFirst(10000, std::vector<Credit>{Credit{3000}, Credit{5000}}) | 2000 |
creditFirst(5000, std::vector<Credit>{Credit{3000}}) | 2000 |
creditFirst(2000, std::vector<Credit>{Credit{5000}}) | 0 |
creditFirst(0, std::vector<Credit>{Credit{1000}}) | 0 |
Hint
Walk the credits, subtract each, and clamp at each step.
Reference solution in C++
int creditFirst(int invoiceTotal, std::vector<Credit> credits) {
int balance = invoiceTotal;
for (const auto& c : credits) { balance -= c.amount; if (balance < 0) balance = 0; }
return balance;
}