Question 1

Complete the code for the myFactorial recursive method shown below, which is intended to compute the factorial of the value passed to the method: public int myFactorial(int anInteger)
{
If (anInteger == 1)
{
Return 1;
}
Else
{
______________________
}
}

Accepted Answer

A)   return(anInteger * (myFactorial(anInteger) ) ) ;
B)   return ((anInteger - 1)  * (myFactorial(anInteger) ) ) ;
C)   return(anInteger * (myFactorial(anInteger - 1) ) ) ;
D)   return((anInteger - 1) *(myFactorial(anInteger - 1) ) ) ; C

Question 2

Consider the method powerOfTwo shown below: public boolean powerOfTwo(int n)
{
If (n == 1) // line #1
{
Return true;
}
Else if (n % 2 == 1) // line #2
{
Return false;
}
Else
{
Return powerOfTwo(n / 2); // line #3
}
}
How many recursive calls are made from the original call of powerOfTwo(64) (not including the original call)?

Accepted Answer

A)   8
B)   6
C)   4
D)   2 B

Question 3

Consider the getArea method from the textbook shown below. public int getArea()
{
If (width <= 0) { return 0; } // line #1
If (width == 1) { return 1; } // line #2
Triangle smallerTriangle = new Triangle(width - 1); // line #3
Int smallerArea = smallerTriangle.getArea(); // line #4
Return smallerArea + width; // line #5
}
Assume that line #2 is changed to this:
If (width == 1) { return 2; }
How would this affect calls to getArea?

Accepted Answer

A)   It would add 1 to all calls except those where width 
B)   It would make no difference to any call.
C)   It would double every triangle area.
D)   It would subtract 1 from all calls. A

Question 4

Consider the getArea method from the textbook shown below. public int getArea()
{
If (width <= 0) { return 0; } // line #1
Else if (width == 1) { return 1; } // line #2
Else
{
Triangle smallerTriangle = new Triangle(width - 1); // line #3
Int smallerArea = smallerTriangle.getArea(); // line #4
Return smallerArea + width; // line #5
}
}
Where is/are the recursive call(s)?

Accepted Answer

A)   line #1
B)   line #2
C)   lines #1 and #2
D)   line #4

Question 5

Consider the method powerOfTwo shown below: public boolean powerOfTwo(int n)
{
If (n == 1) // line #1
{
Return true;
}
Else if (n % 2 == 1) // line #2
{
Return false;
}
Else
{
Return powerOfTwo(n / 2); // line #3
}
}
What is the best interpretation of line #1?

Accepted Answer

A)   One is a power of two
B)   One is not a power of two
C)   Any multiple of one is a power of two
D)   1 is an invalid choice for n

Question 6

Complete the following code snippet, which is intended to print out all permutations of the string generate by using a permutation generator object. public class PermutationGeneratorTester
{
Public static void main(String[] args)
{
PermutationGenerator generator
= new PermutationGenerator("generate");
ArrayList<String> permutations
= generator.getPermutations();
For (String s : permutations)
{
____________________
}
}
}

Accepted Answer

A)   generator.print() ;
B)   generator.setPermutations() ;
C)   generator.calculate() ;
D)   System.out.println(s) ;

Question 7

A palindrome is a word or phrase spelled which reads the same forward or backward. Consider the following code snippet: public boolean palindrome(String string)
{
Return isPal(string, 0, string.length() - 1);
}
Private boolean isPal(String string, int left, int right)
{
If (left >= right)
{
Return true;
}
Else if (string.charAt(left) == string.charAt(right))
{
Return isPal(string, left + 1, right - 1);
}
Else
{
Return false;
}
}
What does the method palindrome return?

Accepted Answer

A)   true
B)   false
C)   a palindrome not found exception
D)   the Boolean value returned from the isPal method

Question 8

Given the following class code: public class RecurseSample
{
Public static void main(String[] args)
{
System.out.println(recurse(3));
}
Public static int recurse(int n)
{
Int total = 0;
If (n == 0)
{
Return 0;
}
Else
{
Total = 3 + recurse(n - 1);
}
Return total;
}
}
What values will be printed when this code is executed?

Accepted Answer

A)   6
B)   9
C)   3, 6, and 9
D)   1, 3, 6, and 9

Question 9

Recursion does NOT take place if any of the following happen:
I method A calls method B, which calls method C, which calls method B
II method A calls method B, which calls method A
III method A calls method B, B returns, and A calls B again

Accepted Answer

A)   I
B)   I and II
C)   II
D)   III

Question 10

A palindrome is a word or phrase that reads the same forward or backward. Consider the following code snippet: public boolean palindrome(String string)
{
Return isPal(string, 0, string.length() - 1);
}
Private boolean isPal(String string, int left, int right)
{
If (left >= right)
{
Return true;
}
Else if (string.charAt(left) == string.charAt(right))
{
Return isPal(string, left + 1, right - 1);
}
Else
{
Return false;
}
}
What is the purpose of the palindrome method?

Accepted Answer

A)   Return the palindrome to the calling method.
B)   Provide the string, along with its first and last indexes to the recursive isPal method.
C)   Send the recursive isPal method its terminating condition.
D)   Recursively call itself.

Question 11

What is required to make a recursive method successful?
I special cases that handle the simplest computations directly
II a recursive call to simplify the computation
III a mutual recursion

Accepted Answer

A)   I
B)   II
C)   I and II
D)   I, II, and III

Question 12

Assume that recursive method search returns true if argument value is one of the elements in the section of the array limited by the firstIndex and lastIndex arguments. What statement can be used in main to determine if the value 7 is one of the elements in array values? public static boolean search(int value, int[] array, int firstIndex, int lastIndex)
{
If (firstIndex <= lastIndex)
{
If (array[firstIndex] == value)
{
Return true;
}
Else
{
Return search(value, array, firstIndex + 1, lastIndex);
}
}
Return false;
}
Public static void main(String[] args)
{
Int [] values = { 4, 7, 1, 0, 2, 7 };
If ( _________________________________ )
{
System.out.println("7 is in the array");
}
}

Accepted Answer

A)   search(7, values, 0, values.length) 
B)   search(7, values, 1, values.length) 
C)   search(7, values, 0, values.length - 1) 
D)   search(7, values, 1, values.length - 1)

Question 13

Consider the method below, which displays the characters from a String in reverse order. Each character appears on a separate line. Select the statement that should be used to complete the method, so that it performs a recursive method call correctly. public static void printReverse(String word)
{
If (word.length() > 0)
{
___________________________
System.out.println(word.charAt(0));
}
}

Accepted Answer

A)   printReverse(word) ;
B)   printReverse(new String(word.charAt(1) ) ) ;
C)   printReverse(word.substring(1) ) ;
D)   printReverse(word.length()  - 1) ;

Question 14

A unique permutation is one that is different from any other generated permutation. How many unique permutations does the string "aaa" have?

Accepted Answer

A)   0
B)   1
C)   2
D)   3

Question 15

____ is a problem-solving technique that examines partial solutions, abandons unsuitable ones, and returns to consider other candidate solutions.

Accepted Answer

A)   Debugging
B)   Traceback
C)   Backtracking
D)   Recursion

Question 16

Consider the fib method from the textbook shown below: public static long fib(int n)
{
If (n <= 2)
{
Return 1;
}
Else
{
Return fib(n - 1) + fib(n - 2);
}
}
Computing the 7th fibonacci number, fib(7), recursively computes fib(6), fib(5), and fib(4) ___ times respectively.

Accepted Answer

A)   1, 2, and 3
B)   6, 5, and 4
C)   4, 5, and 6
D)   3, 2, and 1

Question 17

The method below implements the exponentiation operation recursively by taking advantage of the fact that, if the exponent n is even, then xn = (xn/2)2. Select the expression that should be used to complete the method so that it computes the result correctly. public static double power(double base, double exponent)
{
If (exponent % 2 != 0) // if exponent is odd
{
Return base * power(base, exponent - 1);
}
Else if (exponent > 0)
{
Double temp = ________________________ ;
Return temp * temp;
}
Return base;
}

Accepted Answer

A)   power(base, exponent / 2) 
B)   power(base, exponent / 2)  * power(base, exponent / 2) 
C)   power(base, exponent / 2)  + power(base, exponent / 2) 
D)   power(base, exponent)  / 2

Question 18

Consider the recursive square method shown below that takes a non-negative int argument. public int square(int n)
{
Return square(n, n);
}
Public int square(int c, int n)
{
If (c == 1)
{
Return n;
}
Else
{
Return n + square(c - 1, n);
}
}
Assume that the last return statement is changed to this:
Return n * square(c - 1, n);
What would a call to square(4) return?

Accepted Answer

A)   4
B)   16
C)   64
D)   256

Question 19

Complete the following code snippet, which is intended to be a recursive method that will find the sum of all elements in an array of double values from index to the end of the array: // return the sum of all elements in arr[]
Public static double findSum(double arr[], int index)
{
If (index == 0)
{
_____________________
}
Else
{
Return (arr[index] + findSum(arr, index - 1));
}
}
Assume that this method would be called using an existing array named myArray as follows:
FindSum(myArray,myArray.length - 1);

Accepted Answer

A)   return arr[index];
B)   return arr[index + 1];
C)   return arr[1];
D)   return arr[index - 1];

Question 20

A palindrome is a word or phrase that reads the same forward or backward. Consider the following code snippet: public boolean palindrome(String string)
{
Return isPal(string, 0, string.length() - 1);
}
Private boolean isPal(String string, int left, int right)
{
If (left >= right)
{
Return true;
}
Else if (string.charAt(left) == string.charAt(right))
{
Return isPal(string, left + 1, right - 1);
}
Else
{
Return false;
}
}
What does the condition left >= right refer to?

Accepted Answer

A)   An empty or one-character string is considered a palindrome.
B)   The string is not a palindrome.
C)   It cannot be determined if the string is a palindrome.
D)   You have reached the middle of the string.

Exam 13: Recursion

Complete the code for the myFactorial recursive method shown below, which is intended to compute the factorial of the value passed to the method: public int myFactorial(int anInteger) { If (anInteger == 1) { Return 1; } Else { ______________________ } }

Consider the method powerOfTwo shown below: public boolean powerOfTwo(int n) { If (n == 1) // line #1 { Return true; } Else if (n % 2 == 1) // line #2 { Return false; } Else { Return powerOfTwo(n / 2) ; // line #3 } } What is the best interpretation of line #1?

Recursion does NOT take place if any of the following happen: I method A calls method B, which calls method C, which calls method B II method A calls method B, which calls method A III method A calls method B, B returns, and A calls B again

What is required to make a recursive method successful? I special cases that handle the simplest computations directly II a recursive call to simplify the computation III a mutual recursion

A unique permutation is one that is different from any other generated permutation. How many unique permutations does the string "aaa" have?

____ is a problem-solving technique that examines partial solutions, abandons unsuitable ones, and returns to consider other candidate solutions.

Consider the fib method from the textbook shown below: public static long fib(int n) { If (n <= 2) { Return 1; } Else { Return fib(n - 1) + fib(n - 2) ; } } Computing the 7th fibonacci number, fib(7) , recursively computes fib(6) , fib(5) , and fib(4) ___ times respectively.