leetcode_442

public class  {
    public List<Integer> findDuplicates(int[] nums) {
        List<Integer> list = new ArrayList<>();
        int[] hash = new int[nums.length+1];
        
        for(int i : nums) {
            if( hash[i]++ == 1) {
                list.add(i);
            }
        }
        
        return list;
    }
}