Answer a stack of range totals
A reporting screen asks for the total of many different day ranges over the same series, and asks a lot of them.
- Each query is a pair taken from the two lists by position: `starts[i]` to `ends[i]`.
- Both ends are inclusive.
- A query whose range falls outside the series, or runs backwards, totals 0.
- Return one total per query, in the order the queries came.
RangeTotals(series: list<int>, starts: list<int>, ends: list<int>) → list<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
public List<int> RangeTotals(List<int> series, List<int> starts, List<int> ends) {
}Worked examples
| Call | Result |
|---|---|
RangeTotals(new List<int> { 1, 2, 3, 4, 5 }, new List<int> { 0, 1, 0 }, new List<int> { 2, 3, 4 }) | new List<int> { 6, 9, 15 } |
RangeTotals(new List<int> { 1, 2, 3 }, new List<int> { 1 }, new List<int> { 1 }) | new List<int> { 2 } |
RangeTotals(new List<int> { 1, 2, 3 }, new List<int> { 2 }, new List<int> { 1 }) | new List<int> { 0 } |
RangeTotals(new List<int> { 1, 2, 3 }, new List<int> { 0 }, new List<int> { 99 }) | new List<int> { 0 } |
Hint
Build the running total once, up front. Then any range is one subtraction — the total up to the end, less the total before the start.
Reference solution in C#
public List<int> RangeTotals(List<int> series, List<int> starts, List<int> ends) {
var running = new List<int> { 0 };
foreach (var value in series) running.Add(running[running.Count - 1] + value);
var outList = new List<int>();
for (int i = 0; i < starts.Count; i++) {
int from = starts[i], to = ends[i];
if (from < 0 || to >= series.Count || from > to) outList.Add(0);
else outList.Add(running[to + 1] - running[from]);
}
return outList;
}