class Solution {
public List findDisappearedNumbers(int[] nums) {
Arrays.sort(nums);
List result = new ArrayList<>();
for (int i = 0; i < nums.length; i++) {
int val = Math.abs(nums[i]) - 1;
if (nums[val] > 0) {
nums[val] = -nums[val];
}
}
for (int i = 0; i < nums.length; i++) {
if (nums[i] > 0) {
result.add(i + 1);
}
}
return result;
}
}