Question

void merge(Card[] cardArray, int first, int mid, int last) This is a helper method for the merge sort. It takes as parameters a card array, the first index, the middle index, and the end index. The method merges two adjacent sorted arrays into a single sorted one. The first array begins with the element at first and ends with the element at mid. The second array begins with the element at mid + 1 and ends with the element at last. You will have to use the compares method to make the comparisons.

Answer 1

// method to merge two adjacent sorted arrays into a single sorted one.

void merge(Card[] cardArray, int first, int mid, int last)
{
   int i,j,k;
  
   // create 2 temporary arrays to keep the two arrays (which are sorted)
   Card tempArray1[] = new Card[mid-first+1];
   Card tempArray2[] = new Card[last-mid];

   // Copy the data from cardArray to temp arrays
   for(i=0;i<tempArray1.length;i++)
       tempArray1[i] = cardArray[first+i];
  
   for(j=0;j<tempArray2.length;j++)
       tempArray2[j] = cardArray[mid+1+j];
  
   // merge both the arrays into cardArray in sorted manner
   for(i=0,j=0,k=first;i<tempArray1.length && j <tempArray2.length;)
   {
       // compareTo method to get the smaller card
       if(tempArray1[i].compareTo(tempArray2[j]) < 0)
       {
           cardArray[k] = tempArray1[i];
           i++;
       }else
       {
           cardArray[k] = tempArray2[j];
           j++;
       }
       k++;
   }
  
   // copy the remaining elements from tempArray1 to cardArray
   for(;i<tempArray1.length;i++)
   {
       cardArray[k] = tempArray1[i];
       k++;
   }
  
   // copy the remaining elements from tempArray1 to cardArray
   for(;j<tempArray2.length;j++)
   {
       cardArray[k] = tempArray2[j];
       k++;
   }
}