Chapter 5, Problem 21C

Explanation of Solution

Recursive method to arrange the elements is less than or equal to “n”:

Create the method arrangingElements() that accepts the input parameter as “a”, “n”, “low”, and “high” to arrange the elements is less than or equal to “n” before any integer greater than “n” by calling this method recursively.

Method definition:

//Define the arrangingElements() method

public static void arrangingElements(int a[], int n, int low, int high)

{

  //Check whether the "low" is greater than "high"

  if(low > high)

  {

/*Check whether the "low" is less than array length and "a[low]" is greater than "a[a.length-1]".*/

  if(low < a.length && a[low] > a[a.length - 1])

  {

/*Assign the "a[low]" value to temporary variable. */

  int temp = a[low];

/*Assign the "a[a.length-1]" value to "a[low]". */

  a[low] = a[a.length - 1];

  //Assign the "temp" value to "a[a.length-1]"

  a[a.length - 1] = temp;

  }

//Return it

  return;

  }

/*Otherwise, call arragingElements() method recursively to arrange the elements is less than or equal to "n" before any integer greater than "n". */

  else

  {

  //Check whether the "a[low]" is less than "n"

  if(a[low] < n)

  //Increment "low" by "1"

  low++;

/*Otherwise, check whether "a[low]" is equal to "n". */

  else if(a[low] == n)

  {

/*Check whether "a[a.length-1]" is not equal to than "n". */

  if(a[a.length - 1] != n)

  {

/*Assign the "a[low]" value to temporary variable. */

  int temp = a[low];

/*Assign the "a[a.length-1]" value to "a[low]". */

  a[low] = a[a.length - 1];

/*Assign the "temp" value to "a[a.length-1]"> */

  a[a.length - 1] = temp;

  }

  //Otherwise, increment "low" by "1"

  else

  low++;

}

//Otherwise, swap the array elements

  else

  {

/*Assign the "a[low]" value to temporary variable. */

  int temp = a[low];

//Assign the "a[high]" value to "a[low]"

  a[low] = a[high];

  //Assign the "temp" value to "a[high]"

  a[high] = temp;

  //Decrement "high" by "1"

  high--;

}

/*Call arrangingElements() method recursively to find the elements are less than or equal to "n". */

  arrangingElements(a, n, low, high);

  }

}

Explanation:

In the above code,

• In the arrangingElements() method,
  • It accepts the input parameter as “a”, “n”, “low”, and “high”...