Question

I need to compare between two int arrays of different size.

It has to be most efficient.

Is it possible to do in O(N * log(N)) time?

It should print integers that differ between the two arrays.

Answer 1

The algorithm is O(n), but you are assuming that the arrays are equally sized and each one has a size of ARY_SIZE.

I will not solve the entire homework for you, but I suggest you start with the following function header: int compar2arr(int arrA[], int arrA_size, int arrB[], int arrB_size).

Keep in mind that for function arguments int arrA[] is merely equivalent to int* arrA.

As noted by Keith and Sebastian, arrA_size != arrB_size implies different (unless an author of the task defines it in other way). So you check it at the begining and return false if it holds.

EDIT

Ok, I re-read your post and it seems you need to just display all the not-equal elements and you do not know how to deal with the fact they are of different sizes.

Therefore I suggest to start with the following:

int compar2arr(int arrA[], int arrA_size, int arrB[], int arrB_size)
{
   int smaller_size = // arrA_size or arrB size, the smaller one; 
   int higher_size = // arrA_size or arrB size, the higher one; 
   int *bigger_array;  
   int i;     
   int result = true;

   if (arrA_size > arrB_size)
       bigger_array = arrA;
   else
       bigger_array = arrB;

   for (i = 0; i < smaller_size; i++)
   {
      if (/* i-th elements are not(!!) equal */)
      {
         result = false;
         // print the values to be different
      }
   }

   if (smaller_size != higher_size)
     result = false;

   for (i = smaller_size; i < higher_size; i++)
   {
       // print bigger_array[i]
   }

   return result;
}

I am sure you can come up with the actual code to replace comments.
It is not the most concise way to write, but wanted to keep it easy to understand. Anyway, the computational complexity is O(n), the best possible.