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>
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
List<Integer> reverseReadings(List<Integer> readings) {
}Worked examples
| Call | Result |
|---|---|
reverseReadings(Main.<Integer>ls(1, 2, 3)) | Main.<Integer>ls(3, 2, 1) |
reverseReadings(Main.<Integer>ls(1, 2, 3, 4)) | Main.<Integer>ls(4, 3, 2, 1) |
reverseReadings(Main.<Integer>ls(7)) | Main.<Integer>ls(7) |
reverseReadings(Main.<Integer>ls()) | Main.<Integer>ls() |
Hint
Put one index at each end. Swap what they point at, then step them towards each other until they meet.
Reference solution in Java
List<Integer> reverseReadings(List<Integer> readings) {
List<Integer> out = new ArrayList<>(readings);
int i = 0, j = out.size() - 1;
while (i < j) {
int swap = out.get(i);
out.set(i, out.get(j));
out.set(j, swap);
i++;
j--;
}
return out;
}