public class Solution {
public List<Integer> findDisappearedNumbers(int[] nums) {
int i =0;
int sum = 1;
int prev = 0;
Arrays.sort(nums);
List<Integer> list = new ArrayList<>();
while(i < nums.length){
if(nums[i] == prev){
i++;
}
else if(sum == nums[i]){
prev = nums[i];
sum++;
i++;
}else{
list.add(sum);
sum++;
}
}
while(sum <= nums.length ){
list.add(sum);
sum++;
}
return list;
}
}