Chapter 11

[Skip Breadcrumb Navigation]

Home

Student Resources

Chapter Quizzes

Chapter 11

Recursion

This activity contains 15 questions.

This method is supposed to return the reverse of the string it is given. Which is the correct statement to insert at the indicated line?

String reverse(String s) {
	String result;
	if (s.length() <= 1)
		result = s;
	else
		// What line to insert here?
	return result;
}

result = reverse(s.substring(1, s.length())) 
                 + s.substring(0, 1);

result = reverse(s.substring(0, s.length())) 
                + s.substring(0, 1);

result = s.substring(0, 1)  +
         reverse(s.substring(1,s.length()));

result = s.substring(0, 1)  +
         reverse(s.substring(0,s.length()));

This method is supposed to return true if the String it is given is palindromic (reads the same front-to-back and back-to-front), and returns false otherwise.

What's the missing statement?

boolean palindromic(String s) {
	boolean palin;
	int last = s.length() - 1;
	if (s.length() <= 1)
		palin = true;
	else if // missing statement goes here
	else
		palin = false;	
	return palin;
}

else if (s.substring(0, 1).compareTo(
         s.substring(last)) == 1)
    palin = palindromic(
             s.substring(1, last));

else if (s.substring(0, 1). ==
         s.substring(last))
    palin = palindromic(
             s.substring(1, last));

else if (s.substring(1, 1).compareTo(
         s.substring(last)) == 0)
    palin = palindromic(
         s.substring(0, last));

else if (s.substring(0, 1).compareTo(
         s.substring(last)) == 0)
    palin = palindromic(
         s.substring(1, last));

What does this program print?

public class NFactorial {

	NFactorial() {
		for (long n = 1; n <= 6; n++)
			System.out.println(n + "! = " +
				factorial(n));
	}

	long factorial(long n) {
		long nfactorial = 
			(n <= 1) ? 1 : n*factorial(n-1);
		return nfactorial;
	}
	
	public static void main(String[] args) {
		new NFactorial();
	}
}

1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
0! = 0
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720

What does this program print?

public class Recursive {

	Recursive() {
		System.out.println(calcA(3, 4));
	}

	int calcA(int a, int b) {
		return (a * b == 0) ? 0 :
					calcB(calcA(a, b-1), b);
	}

	int calcB(int a, int b) {
		return (b <= 0) ? a : 
						  1 + calcB(a, b-1);
	}

	public static void main(String[] args) {
		new Recursive();
	}
}

610127

What is printed?

public class Recurse {

	Recurse() {
		int[] a = { 12, 23, 34, 45,
				    56, 67, 78 };
		System.out.println(
			search(a, 0, a.length-1, 40)
			+ " " +
			search(a, 0, a.length-1, 56));
	}

	int search(int[] a, 
			int frst, int last, int key) {
		int mid = (frst + last) / 2;
		return 
			(frst > last)   ? -1 :
			(key == a[mid]) ? a[mid] :
			(key <  a[mid]) ? 
			   search(a, frst, mid-1, key) :
			   search(a, mid+1, last, key);
	}

	public static void main(String[] args) {
		new Recurse();
	}

}

-1 -140 56-1 5640 -1

What is printed?

public class Recurse {

	Recurse() {
		int[] a = { 3, 1, 4, 1, 
					5, 9, 2, 6, 5 };
		System.out.println(
					find(a, a.length - 1));
	}

	int find(int[] a, final int n) {
		int ans = 0;
		if (n >= 0) {
			ans = ma(a[n], find(a, n-1));
		}
		return ans;
	}

	int ma(final int a, final int b) {
		return (a > b) ? a : b;
	}

	public static void main(String[] args) {
		new Recurse();
	}

}

1395

What is printed?

public class Recurse {

	Recurse() {
		System.out.println(gc(18, 27));
		System.out.println(gc(61, 53));
		System.out.println(gc(98, 868));
	}

	int gc(final int a, final int b) {
		return (b == 0) ? a : gc(b, a % b);
	}

	public static void main(String[] args) {
		new Recurse();
	}

}

18
61
989
1
1418
2
2818
53
98

What is printed?

public class Recurse {

	Recurse() {
		System.out.println(pw(3, 5));
	}

	int pw(final int a, final int b) {
		int c = 1;
		if (b > 0) {
			if (b % 2 == 0)
				c = pw(a * a, b / 2);
			else {
				c = a * pw(a, b - 1);
			}
		}
		return c;
	}

	public static void main(String[] args) {
		new Recurse();
	}

}

312524381

What is printed?

public class Recurse {

	Recurse() {
		System.out.println(dog("abcd",
							   "EFG"));
	}

	String dog(String s, String t) {
		String ans = "";
		if (t == null || t.length() <= 0)
			ans = s;
		else
			ans = dog(s + 
					 t.charAt(t.length()-1),
					 t.substring(0, 
							 t.length()-1));
		return ans;
	}

	public static void main(String[] args) {
		new Recurse();
	}

}

abcdGFEabcdEFGGFEdcbaEFGdcba

What is printed?

public class Recursive {

	Recursive() {
		for (int n = 1; n < 3; n++)
			for (int k = 1; k < 3; k++)
				System.out.println(
					n + " " + k + " = " +
					calc(n, k));
	}

	int calc(int a, int b) {
		int result = a;
		if (b > 0)
			result = calc(a+1, b-1);
		return result;
	}
	
	public static void main(String[] args) {
		new Recursive();
	}
}

0 0 = 0
0 1 = 0
1 0 = 0
1 1 = 1
1 2 = 2
2 1 = 2
2 2 = 4
1 1 = 1
1 2 = 2
2 1 = 2
2 2 = 4
1 1 = 2
1 2 = 3
2 1 = 3
2 2 = 4
0 0 = 0
0 1 = 1
1 0 = 1
1 1 = 2
1 2 = 3
2 1 = 3
2 2 = 4

What is printed?

public class Recursive {

	Recursive() {
		System.out.println(calcA(3, 4));
	}

	int calcA(int a, int b) {
		return (a * b == 0) ? 0 :
					calcB(calcA(a-1, b), b);
	}

	int calcB(int a, int b) {
		return (b <= 0) ? a : 
							calcB(a+1, b-1);
	}

	public static void main(String[] args) {
		new Recursive();
	}
}

672012

What is printed?

public class Recursive {

	Recursive() {
		System.out.println(Ack(2, 3));
	}
		
	long Ack(long m, long n) {
		long result;
		if (m <= 0)
			result = n+1;
		else if (n <= 0)
			result = Ack(m-1, 1);
		else
			result = Ack(m-1, Ack(m, n-1));
		return result;
	}

	public static void main(String[] args) {
		new Recursive();
	}
}

116179

What is printed?

public class Recursive {

	Recursive() {
		System.out.println(Back(2, 3));
	}
		
	long Back(long m, long n) {
		return (m <= 0) ? n+1 :
			   (n <= 0) ? Back(m-1, 1) :
				     Back(m-1,Back(m, n-1));
	}

	public static void main(String[] args) {
		new Recursive();
	}
}

9611212

What is printed?

public class Recursive {

	Recursive() {
		System.out.println(fib(7));
	}

	int fib(int n) {
		return (n <= 1) ? n :
			   fib(n-1) + fib(n-2);
	}

	public static void main(String[] args) {
		new Recursive();
	}
}

8122113

Which statements are true?

Direct recursion occurs when a method calls itself.
Indirect recursion occurs when a method calls itself.
Indirect recursion requires the existence of at least two methods.
Direct recursion can experience infinite recursion, while indirect recursion cannot.
Indirect recursion can experience infinite recursion, while direct recursion cannot.

True: a, c, e.True: a, c.True: b, c.True: a, c, d.

The Submit Answers for Grading feature requires scripting to function. Your browser either does not support scripting or you have turned scripting off.

So, the Submit Answers for Grading button below will not work.

The following Submit Answers for Grading button is provided in its place and will clear your answers:
The Clear Answers and Start Over feature requires scripting to function. Your browser either does not support scripting or you have turned scripting off.

So, the Clear Answers and Start Over button below will not work.

The following Clear Answers button is provided in its place and will clear your answers:

Your browser either does not support scripting or you have turned scripting off. Because of this, the answer choices will NOT appear in a different order each time the page is loaded, though that is mentioned below. Note that you do not need this feature to use this site.

Answer choices in this exercise appear in a different order each time the page is loaded.

Chapter 11

This method is supposed to return the reverse of the string it is given. Which is the correct statement to insert at the indicated line?
String reverse(String s) { String result; if (s.length() <= 1) result = s; else // What line to insert here? return result; }

What is printed?
public class Recursive { Recursive() { System.out.println(fib(7)); } int fib(int n) { return (n <= 1) ? n : fib(n-1) + fib(n-2); } public static void main(String[] args) { new Recursive(); } }

Chapter 11

This method is supposed to return the reverse of the string it is given. Which is the correct statement to insert at the indicated line? String reverse(String s) { String result; if (s.length() <= 1) result = s; else // What line to insert here? return result; }

What is printed? public class Recursive { Recursive() { System.out.println(fib(7)); } int fib(int n) { return (n <= 1) ? n : fib(n-1) + fib(n-2); } public static void main(String[] args) { new Recursive(); } }

This method is supposed to return the reverse of the string it is given. Which is the correct statement to insert at the indicated line?
String reverse(String s) { String result; if (s.length() <= 1) result = s; else // What line to insert here? return result; }

What is printed?
public class Recursive { Recursive() { System.out.println(fib(7)); } int fib(int n) { return (n <= 1) ? n : fib(n-1) + fib(n-2); } public static void main(String[] args) { new Recursive(); } }