Chapter 5, Problem 23C

Explanation of Solution

Recursive method to determine the sum of two elements is equal to “n”:

Create the method checkSum() that accepts the input parameter as “A”, “j”, and “k” to determine the sum of two elements in an array “A” is equal to “A[i]” by calling this method recursively.

Method definition:

//Define the checkSum() method

public static boolean checkSum(int A[], int j, int k)

{

  //Loop executes until the array length

  for (int i = 0; i < A.length; i++)

  {

  //Check whether "j" and "k" is less than "i"

  if((i > j) && (k < i))

  {

/*Check whether sum of "A[j]" and "A[k]" is equal to "A[i]". */

  if (A[i] == A[j] + A[k])

  {

/*Return true, if there are elements in array "A" that sum is equal to "A[i]". */

  return true;

  }

  }

  }

//Check whether "k+1" is equal to length of array

  if (k + 1 == A.length)

  {

/*Check whether "j+1" is less than to length of array. */

  if (j + 1 < A.length)

  {

/*Call checkSum() method recursively by passing the parameters as "A", "j+1", and "0" to sum the two elements is equal to "A[i]" and return it */

  return checkSum(A, j + 1, 0);

  }

/*Return true, if there are no elements in array "A" that sum is equal to "A[i]"...