Question

1) Write a Java pseudocode that uses recursion to accomplish the task. Here is a hint. When you are searching for a particular value in an array, there are two possible outcomes.

a. The value is found and the array index of that value is returned.

b. The value is not found and we return -1.

2) Convert the pseudocode in (1) above into a working Java program.

Answer 1

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PseudoCode

Main

Step 1: Start

Step 2:Declare and initialize input array.

Step 3: Declare and initialize the search key.

Step 4: Call the recursive function index=recSearch(a, 0, a.length-1, key)

Step 5:If index!=1, then the value is found . Otherwise, The value is not found .

Step 6: Stop

Function recSearch(int arr[], int l, int r, int x)
    Step 1:    if (r < l)     return -1
    Step 2: if (arr[l] == x)     return l
    Step 3: if (arr[r] == x)       return r
    Step 4: Otherwise    call recursive function recSearch(arr, l+1, r-1, x);
    Step 5: Stop

Program

import java.util.Scanner;

public class Main
{
public static void main(String args[])
   {
      int i,key=9;
      int a[]={1,4,7,9,10};   
      int index = recSearch(a, 0, a.length-1, key);
      if (index != -1)
           System.out.println("Element " + key + " is present at index " +
                                                    index);
        else
            System.out.println("Element " + key + " is not present");
   }
public static int recSearch(int arr[], int l, int r, int x)
     {
          if (r < l)
             return -1;
          if (arr[l] == x)
             return l;
          if (arr[r] == x)
             return r;
          return recSearch(arr, l+1, r-1, x);
     }
}

Output

Element 9 is present at index 3