static int f(int[] nums, int n){ List<integer> l = Arrays.stream(nums).distinct().sorted().boxed().collect(Collectors.toList()); if (l.size() < 2 * n) return -1; int ans = 0; for (int i = 0; i < n; i++) { ans += l.get(i) + l.get(l.size() - 1 - i); } return ans; }</integer>