Recursion Post Test

Knowledge/Memory:

1. Which of the following statements are true?

 
I. A recursive method is a method that calls itself.
II. A recursive solution is always more complex than its equivalent iterative solution.
III. Recursion is a special type of repetition control.
IV. A recursive solution is always more efficient than its equivalent iterative solution.
 
a.  I & II
b.  I, II & III
c.  I, II & IV
d.  I & III
e.  II & IV

Answer: D

2. It is appropriate to use recursion if

a. A recursive solution is natural and easy to understand.

b. A recursive solution does not result in excessive duplicate computation.

c. The equivalent iterative solution is too complex.

d. All of the above.

Answer: D

3. The basic elements of a recursive method are:

I. A test to stop or continue the recursion.

II. A test to verify the method logic.

III. An end case that terminates the program.

IV. An end case that terminates the recursion.

V. Recursive call(s) that continues the recursion.

a. I, II & III

b. I, II & V

c. I, IV & V

d. II, III & V

Answer: C

Comprehension:

4. You have an iterative Java method, computeTotal(). When is it possible to write a recursive version of computeTotal()?

a. It is always possible to write a recursive version of computeTotal().

b. It is generally possible to write a recursive version of computeTotal().

c. It is rarely possible to write a recursive version of computeTotal().

d. It is never possible to write a recursive version of computeTotal().

Answer: A

Application:

5. Given the following recursive Java code that lists the contents of a directory on your hard drive (including the contents of any subdirectories):

1 public void directoryListing(File file){

2

3 String [] fileList;

4 String pathname = file.getAbsolutePath();

5

6 if (file.isFile()) {

7 System.out.println(file.getName());

8 } else {

10 fileList = file.list();

11 for (int i = 0; i < fileList.length; i++){

12 File nextFile = new File(pathname + File.separator + fileList[i]);

13 directoryListing(nextFile);

14 } /* for */

15 } /* else */

16 }

Which line contains the test condition?

1. Line 4
2. Line 6
3. Line 10
4. Line 12

Answer: B

6. Given the following recursive Java code that lists the contents of a directory on your hard drive (including the contents of any subdirectories):

1 public void directoryListing(File file){

2

3 String [] fileList;

4 String pathname = file.getAbsolutePath();

5

6 if (file.isFile()) {

7 System.out.println(file.getName());

8 } else {

10 fileList = file.list();

11 for (int i = 0; i < fileList.length; i++){

12 File nextFile = new File(pathname + File.separator + fileList[i]);

13 directoryListing(nextFile);

14 } /* for */

15 } /* else */

16 }

Which line contains the end case?

1. Line 7
2. Line 10
3. Line 12
4. Line 13

Answer: A

7. Given the following recursive Java code that lists the contents of a directory on your hard drive (including the contents of any subdirectories):

1 public void directoryListing(File file){

2

3 String [] fileList;

4 String pathname = file.getAbsolutePath();

5

6 if (file.isFile()) {

7 System.out.println(file.getName());

8 } else {

10 fileList = file.list();

11 for (int i = 0; i < fileList.length; i++){

12 File nextFile = new File(pathname + File.separator + fileList[i]);

13 directoryListing(nextFile);

14 } /* for */

15 } /* else */

16 }

Which line contains the recursive call?

1. Line 7
2. Line 10
3. Line 12
4. Line 13

Answer: C

8. Given the following method, recurse():

int recurse(int v)
{
 if (v>6) return recurse(v);
 return v;

}

Which of the following statements is true?

a. The method will always terminate properly.

b. When v is initialized to a value of 6 or less, the method will never begin to recurse; when v is initialized to a value greater than 6, it will not terminate.

c. The method will never terminate properly.

d. The method will terminate only when the parameter to the method is greater than 6.

Answer: B

9. Given the following recursive function definition for compute():

compute(a, 0) = 1

compute(a, n) = a * compute(a, n-1);

What is the result of compute(3,4)?

a. 0

b. 81

c. 64

d. 27

e. 12

Answer: B

10. Given the following recursive function definition, div(), for integers N and M:

div( N, M ) = 0, if N < M

div( N, M ) = 1 + div( N-M, M ), if N >= M

Assume 0 <= N and 0 < M. Which of the following code segments correctly implements div()?

a) int div( int N, int M ) {

  if ( N < M )
   return N;
  else
   return div( N-M, M );
 }
 

b) int div( int N, int M ) {

  if ( N == M )
   return N;
  else
   return div( N-M, M );
 }

c) int div( int N, int M ) {

   if ( N < M )
   return 0;
  else
   return 1+div( N-M, N );
  }

d) int div( int N, int M ) {

   if ( N < M )
   return 0;
   else
   return 1+div( N-M, M );
 }

Answer: D