/* Java class containing static methods that perform elementwise sum and
** difference upon on arrays of type int[] (i.e., arrays of int values).
**
**  Author: R. McCloskey
**  last updated : October 2022
*/
public class ArrayUtils {

   /* Returns a new array each of whose elements is the sum of the
   ** corresponding elements in the two given arrays (a[] and b[]).
   ** (In case a.length and b.length differ, we imagine that the shorter
   ** array is "expanded" to the other one's length and that the "new"
   ** elements have value zero.)
   ** To be precise, the array returned, call it c[], has these properties:
   **   c.length == N
   **   c[i] == a[i] + b[i] for all i in 0..M-1,
   **   c[i] == a[i] for all i in M..a.length-1, and
   **   c[i] == b[i] for all i in M..b.length-1,
   ** where M = min(a.length, b.length) and N = max(a.length, b.length) 
   */
   public static int[] sumElementWise(int[] a, int[] b) {
      final int M = Math.min(a.length, b.length);
      final int N = Math.max(a.length, b.length);

      int[] c = new int[N];

      // Sum elements at corresponding locations in a[] and b[] and place 
      // result into corresponding location of c[].
      for (int i=0; i != M; i++) { 
         c[i] = a[i] + b[i];
      }

      // Now copy into c[] the remaining elements of the longer array.
      for (int i=M; i != a.length; i++) { c[i] = a[i]; }
      for (int i=M; i != b.length; i++) { c[i] = b[i]; }
 
      return c;
   }

   /* Returns a new array each of whose elements is the difference of the
   ** corresponding elements in the two given arrays (a[] and b[]).
   ** (In case a.length and b.length differ, we imagine that the shorter
   ** array is "expanded" to the other one's length and that the "new"
   ** elements have value zero.)
   ** To be precise, the array returned, call it c[], has these properties:
   **   c.length == N
   **   c[i] == a[i] - b[i] for all i in 0..M-1,
   **   c[i] == a[i] for all i in M..a.length-1, and
   **   c[i] == b[i] for all i in M..b.length-1,
   ** where M = min(a.length, b.length) and N = max(a.length, b.length) 
   */
   public static int[] differenceElementWise(int[] a, int[] b) {
      final int M = Math.min(a.length, b.length);
      final int N = Math.max(a.length, b.length);

      int[] c = new int[N];

      // Take difference of elements at corresponding locations in a[] and b[]
      // and place result into corresponding location of c[].
      for (int i=0; i != M; i++) { 
         c[i] = a[i] - b[i];
      }

      // Now copy into c[] the remaining elements of the longer array.
      for (int i=M; i != a.length; i++) { c[i] = a[i]; }
      for (int i=M; i != b.length; i++) { c[i] = -b[i]; }
 
      return c;
   }

}  // end of class