Question

Question 6)

A “Golomb ruler” is a collection of integers such that no two pairs of values are the same distance apart. Eg: If the current ruler is {1, 2, 4}, then either 7 or 9 could be added to the ruler but not both.

(Since 7 − 2 = 5 and 9 − 4 = 5).
You might want to use Math.abs(n) to compute the absolute value of n and the sort(null) method on List to sort a list.

public class Ruler {

/**
* Creates a ruler containing no values
*/
public Ruler();

/**
* @return The values of in the ruler (in increasing order), comma separated.
* This method should not rearrange/reorder any internal data.
*/
public String toString();

/**
* @return true if x could be added to the ruler without breaking the invariant,
* false otherwise
*/
public boolean isLegal(int x);

/**
* Add x to the ruler if doing so wouldn’t break the invariant, do nothing otherwise.
*/
public void add(int x);
}

A) Which Javadoc tag should be used on add(int x) to describe the invariant?

B) Declare the member variables you think are necessary.

C) Implement toString() for this class.

D) Implement isLegal() for this class.

E) Implement add(int x) for this class.

Answer 1

Thanks for posting the question, we are glad to help you. Below is the Java class - Ruler.java where all the methods has been implemented as asked in the question.

The class also has the main() method which is used to run the program and its works as expected : )

Thats It !!! Refer the screenshot for the output the program generated when i ran the program : )

Here is the class -

--------------------------------------------------------------------------------------------------------------------------------

import java.util.ArrayList;

public class Ruler {

// B) Declare the member variables you think are necessary.

private ArrayList<Integer> scale;

private ArrayList<Integer> differences;

/**

* Creates a ruler containing no values

*/

public Ruler() {

scale = new ArrayList<Integer>();

differences = new ArrayList<Integer>();

}

/**

* @return The values of in the ruler (in increasing order), comma separated.

*

* This method should not rearrange/reorder any internal data.

*/

// C) Implement toString() for this class.

public String toString() {

String ruler = "{";

for (int item : scale) {

ruler += item + ", ";

}

ruler = ruler.substring(0, ruler.length() - 2) + "}";

return ruler;

}

/**

* @return true if x could be added to the ruler without breaking the invariant,

* false otherwise

*/

// D) Implement isLegal() for this class.

public boolean isLegal(int x) {

boolean isTheDifferenceExists = false;

for (int item : scale) {

int difference = Math.abs(item - x);

int index = differences.indexOf(difference);

if (index >= 0) {

isTheDifferenceExists = true;

break;

}

}

return !isTheDifferenceExists;

}

/**

* Add x to the ruler if doing so wouldn’t break the invariant, do nothing

* otherwise.

*/

// E) Implement add(int x) for this class.

public void add(int x) {

boolean isTheDifferenceExists = false;

for (int item : scale) {

int difference = Math.abs(item - x);

int index = differences.indexOf(difference);

if (index >= 0) {

isTheDifferenceExists = true;

break;

}

}

if (!isTheDifferenceExists) {

for (int item : scale) {

differences.add(Math.abs(item - x));

}

scale.add(x);

}

}

public static void main(String[] args) {

Ruler ruler = new Ruler();

ruler.add(1);

System.out.println(ruler);

ruler.add(2);

System.out.println(ruler);

ruler.add(4);

System.out.println(ruler);

ruler.add(5);

System.out.println(ruler);

ruler.add(9);

System.out.println(ruler);

}

}

--------------------------------------------------------------------------------------------------------------------------------

Image Screenshot

thank You !!!!

plz a thumbs up : )