Question

instructions

These questions should test if you have understood the contents of Chapter 18 "Recursion".

1. What will this method return if you call it this: xMethod (4)

static int xMethod (int n) { 
  if (n == 1) 
   return 1; 
  else 
   return n + xMethod (n - 1); 
}

1. 10

2. 11

3. 12

4. 9

2. Analyze the following code:

public class Test { 
  public static void main (String [] args) { 
    int [] x = {1, 2, 3, 4, 5}; 
    xMethod (x, 5); 
  } 
  public static void xMethod (int [] x, int length) { 
    System.out.print (x [length - 1] + ""); 
    xMethod (x, length - 1); 
  } 
}

1. The program will display 5 4 3 2 1

2. The program will display 1 2 3 4 5

3. The program will display 5 4 3 2 1 and cast an ArrayIndexOutOfBoundsException

4. The program will display 1 2 3 4 5 and cast an ArrayIndexOutOfBoundsException

3. What must return value be for the isPalindrome to use the help method correctly?

public static boolean isPalindrome (String s) { 
  return isPalindrome (s, 0, s.length () - 1); 
} 
public static boolean isPalindrome (String s, int low, int high) { 
  if (high <= low) 
    return true; 
  else if (s.charAt (low)! = s.charAt (high)) 
    return false; 
  else 
    return _______________________________; 
}

1. isPalindrome (s, low, high - 1)

2. isPalindrome (s)

3. isPalindrome (s, low, high)

4. isPalindrome (s, low + 1, high - 1)

5. isPalindrome (s, low + 1, high)

4. What must the check be for this method to check if the text string is a palindrome?

public static boolean isPalindrome (String s) { 
  if (s.length () <= 1) // Base case 
    return true; 
  else if _____________________________ 
    return false; 
  else 
    return isPalindrome (s.substring (1, s.length () - 1)); 
}

1. (s.charAt (1)! = s.charAt (s.length ()))

2. (s.charAt (0)! = s.charAt (s.length () - 1))

3. (s.charAt (0)! = s.charAt (s.length ()))

4. (s.charAt (1)! = s.charAt (s.length () - 1))

5. With the code of the Tower of Hanoi as shown in the book, how many times will the moveDisks method be called 3 disks?

1. 14

2. 3

3. 7

4. 10

6. Analyze the code for the following program:

A:

public class Test { 
  public static void main (String [] args) { 
    xMethod (5); 
  } 
  public static void xMethod (int length) { 
    if (length> 1) { 
      System.out.print ((length - 1) + ""); 
      xMethod (length - 1); 
    } 
  } 
}

B:

public class Test { 
  public static void main (String [] args) { 
    xMethod (5); 
  } 
  public static void xMethod (int length) { 
    while (length> 1) { 
      System.out.print ((length - 1) + ""); 
      xMethod (length - 1); 
    } 
  } 
}

1. Both programs will print 1 2 3 4 5 for display.

2. A will end normally while B will endlessly.

3. B will end normally while A will endlessly.

4. Both programs will print 5 4 3 2 1 for display.

5. Both programs will print 4 3 2 1 for display.

6. Both programs will print 1 2 3 4 for display.

7. Which of the following are true ?

1. Recursive methods run faster than iterative methods.

2. Recursive methods often take up more memory than iterative methods.

3. Recursive methods can always be replaced with iterative methods.

4. In some cases, recursive methods will provide much more natural and simpler solutions, while other solutions may be ugly and difficult.

8. What will the following class print?

public class Test1 { 
  public static void main (String [] args) { 
    System.out.println (f2 (2, 0)); 
  } 
  public static int f2 (int n, int result) { 
    if (n == 0) 
      return 0; 
    else 
      return f2 (n - 1, n + result); 
  } 
}

1. 0

2. 1

3. 3

4. 2

Answer 1

1.
1. 10

2.
3. The program will display 5 4 3 2 1 and cast an ArrayIndexOutOfBoundsException

3.
4. isPalindrome (s, low + 1, high - 1)

4.
2. (s.charAt (0)! = s.charAt (s.length () - 1))

5.
3. 7

6.
2. A will end normally while B will endlessly.

7.
2. Recursive methods often take up more memory than iterative methods.

8.
1. 0