The middle of the list
A dashboard shows a campaign’s typical daily spend, and “typical” is whatever lands in the middle once the days are sorted.
- An odd number of readings: the middle one, once sorted.
- An even number: the average of the two middle ones.
- An empty list has no middle: return zero.
medianOf(values: list<int>) → float
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
double medianOf(List<Integer> values) {
}Worked examples
| Call | Result |
|---|---|
medianOf(Main.<Integer>ls(3, 1, 2)) | 2.0 |
medianOf(Main.<Integer>ls(1, 2)) | 1.5 |
medianOf(Main.<Integer>ls(5)) | 5.0 |
medianOf(Main.<Integer>ls(5, 1, 4, 2)) | 3.0 |
Hint
Sort a copy, not the caller’s list, then look at the middle pair or single value.
Reference solution in Java
double medianOf(List<Integer> values) {
List<Integer> xs = new ArrayList<>(values);
Collections.sort(xs);
int n = xs.size();
if (n == 0) return 0.0;
int mid = n / 2;
return n % 2 == 1 ? xs.get(mid) : (xs.get(mid - 1) + xs.get(mid)) / 2.0;
}