class Solution {
    public List<Integer> findDisappearedNumbers(int[] nums) {
        List<Integer> res=new ArrayList<>();
        int[] count=new int[nums.length+1];
        
        for(int num:nums)
            count[num]++;
        
        for(int i=1; i<count.length; i++){
            if(count[i]==0)
                res.add(i);
        }
        
        return res;
    }
}