Finding missing elements in an array

Question

Given you have an array A[1..n] of size n, it contains elements from the set {1..n}. However, two of the elements are missing, (and perhaps two of the array elements are rep

Answer 1

As we know we are looking for elements between 1 to N Create a Hash set containing 1 to N.

foreach(int i in input)
{
   if(hashset.contains(i))
   {
      hashset.delete(i);
   }
}

return "remaining elements in Hashset.";

The remaining elements in Hashset are the missing elements.