Question

The code snippet below is an example of pass by reference. We also provide a sample method
setZeroAt, which sets 0 at a position i in the array, to illustrate pass by reference.
 
  public class Sample {
      public static void setZeroAt(int [] arr, int i){
        arr[i] = 0;
      }

      public static void main(String[] args) {
             Scanner input = new Scanner(System.in);
             int sample[] = {1, 2, 3};
             setZeroAt(sample, 1);
             //Now sample looks like {1, 0, 3}
      }
  }
 
Write a Java method that takes an array and two integer indices a and b. If a and b are
valid integer indices for the array, swap the values in that position.
 
Also ensure that the two indices are valid. If not, do not swap the values. Remember that
when you pass an array as a parameter, it is passed by reference.  Use the code snippet below.
 
For example, consider the array {0, 1, 2, 3}. For a = 0, b = 2, the swapped array must be
{2, 1, 0, 3}. You can swap with a = 2, b = 0 on the original array to get the same result.
 
import java.util.Scanner;

public class SwapArrayIndex {
     
      public static void print_array(int [] arr){
              for(int i = 0; i < arr.length; ++i)
                     System.out.print(arr[i]+" ");
              System.out.println();
      }
      public static void main(String[] args) {
              Scanner input = new Scanner(System.in);
              //Start of Sample Code
              int sample[] = {1, 2, 3};
              setZeroAt(sample, 1);
              //Now sample looks like {1, 0, 3}
              //End of Sample Code
              int arr[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
              print_array(arr);
              int a = input.nextInt();
              int b = input.nextInt();
              swap(arr, a, b);
              print_array(arr);
      }
}


Part B: Random Shuffling
------------------------
Use swap method to perform random shuffling. Write a shuffle method that takes an array. It
generates two valid indices randomly, that can be swapped and calls the swap method to swap
the positions in the array. Look at question 1 for generating a valid index (but look out for
an obvious pitfall).