Reverse a list end to end
A replay view shows the most recent reading first, so the buffer has to come back the other way round.
- The order reverses; the values themselves are untouched.
- An empty list and a single reading both come back as they went in.
ReverseReadings(readings: 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> ReverseReadings(List<int> readings) {
}Worked examples
| Call | Result |
|---|---|
ReverseReadings(new List<int> { 1, 2, 3 }) | new List<int> { 3, 2, 1 } |
ReverseReadings(new List<int> { 1, 2, 3, 4 }) | new List<int> { 4, 3, 2, 1 } |
ReverseReadings(new List<int> { 7 }) | new List<int> { 7 } |
ReverseReadings(new List<int> { }) | new List<int> { } |
Hint
Put one index at each end. Swap what they point at, then step them towards each other until they meet.
Reference solution in C#
public List<int> ReverseReadings(List<int> readings) {
var outList = new List<int>(readings);
int i = 0, j = outList.Count - 1;
while (i < j) {
int swap = outList[i];
outList[i] = outList[j];
outList[j] = swap;
i++;
j--;
}
return outList;
}