Question

1. Convert the following recursive method to be tail-recursive
2. Explain what is the advantage of a recursive method to be tail-recursive.

public int f8( int[] arr, int index )
{
   if ( index == -1 )
      return 0;
   if (arr[index] == 2)
      return 1 + f8( arr, index - 1 );
   return f8( arr, index - 1);
}

Answer 1

ff8() is the tail recursive method

uses of tail recursion:

uses less memory and less stack frames.

import java.util.*;

class Hello {

    public int f8(int[] arr, int index) {

        if (index == -1)

            return 0;

        if (arr[index] == 2)

            return 1 + f8(arr, index - 1);

        return f8(arr, index - 1);

    }

    public int ff8(int[] arr, int index, int count) {

        if (index == -1)

            return count;

        if (arr[index] == 2)

            return ff8(arr, index - 1, count + 1);

        return ff8(arr, index - 1, count);

    }

    public static void main(String[] args) {

        int[] a = { 1, 2, 3, 2, 5 };

        Hello h = new Hello();

        System.out.println(h.f8(a, 4));

        System.out.println(h.ff8(a, 4, 0));

    }

}