Totals per category
A ledger groups every sale under its category so each bucket shows a single sum.
- Add the amounts of every sale under the same category.
- Every category that appears earns an entry in the result.
- The result is one running total per category.
sumPerCategory(sales: list<Sale>) → map<string, int>
Java 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
Map<String, Integer> sumPerCategory(List<Sale> sales) {
}Worked examples
| Call | Result |
|---|---|
sumPerCategory(Main.<Sale>ls(new Sale("food", 10), new Sale("food", 15))) | Main.<String, Integer>mp("food", 25) |
sumPerCategory(Main.<Sale>ls(new Sale("a", 3), new Sale("b", 4), new Sale("a", 5))) | Main.<String, Integer>mp("a", 8, "b", 4) |
sumPerCategory(Main.<Sale>ls(new Sale("x", 1))) | Main.<String, Integer>mp("x", 1) |
sumPerCategory(Main.<Sale>ls(new Sale("p", 0), new Sale("q", -2))) | Main.<String, Integer>mp("p", 0, "q", -2) |
Hint
Aggregate into a map keyed by category, adding each amount as you go.
Reference solution in Java
Map<String, Integer> sumPerCategory(List<Sale> sales) {
Map<String, Integer> result = new LinkedHashMap<>();
for (Sale s : sales) result.merge(s.category, s.amount, Integer::sum);
return result;
}