Create a concrete LinkedList class that extends the provided ALinkedList class. You will need to override the extract()method in your class. You can use your main() method for testing your method (although you do not need to provide a main method).

Recall that a list is an ordered collection of data

X_0, X_1, X_2, ..., X_n-1

The extract(int start, int end) method removes all elements

X_start, X_start_1, ..., X_end-1

from the list. It also returns all removed elements as a new list (LinkedList) that retains the same ordering.

For example, if the initial list called animals was

cat, dog, eel, cow, owl, pig, pip

then animals.extract(1,5) would return the new list

dog, eel, cow, owl

and animals would now be the list

cat, pig, pip

The AlinkedList class also has a sort() method that currently does nothing. Complete this method so that it sorts the current linked list (alphabetically).

For example, if there was a list called kids that consisted of puppy, kitten, cub, leveret, kit, cygnet then after calling kids.sort(), the list would now be cub, cygnet, kit, kitten, leveret, puppy

This is the code:

public abstract class ALinkedList{

public Node head;

public Node tail;

public int size;

/** removes and returns the sublist

* [x_start, x_start+1, ..., x_end-1] from the current list

*

* @param start is the starting position of the list to remove.

* You can assume that 0 <= start <= length of list -1.

* @param end is position after the last element to be removed.

* You can assume that start <= end <= length of list.

*/

public abstract ALinkedList extract(int start, int end);

/** Sorts this list

<p>

This method sorts this list lexicographically (alphabetically).

Use the built-in compareTo() in the String class to compare individual strings in the list.

<p>

You are NOT allowed to use any sort method provided in java.util.Arrays or java.util.Collections.

*/

public void sort(){}

/* -----------------------------------------

provided code

----------------------------------------- */

/** returns the size of the list

*

* @return the size of the list

*/

public final int size(){ return size; }

public final String get(int position){

// returns data of element at index position

// returns null otherwise

if( position < 0 || position > size -1 || head == null){

return null;

}

int count = 0;

Node current = head;

while(count < position){

current = current.getNext();

count += 1;

}

return current.get();

}

/** add a string to the back of the list

*

* @param s is a string to add to the back of the list

* @return the current list

*/

public final ALinkedList add(String s){

if( size == 0 ){

head = tail = new Node(s, null);

}else{

Node tmp = new Node(s, null);

tail.setNext(tmp);

tail = tmp;

}

size += 1;

return this;

}

public final ALinkedList add(int position, String d){

// add a new node with data d at given position

// return null if method fails

if( position < 0 || position > size){

return null;

}

if( position == 0){

return addFront(d);

}else if( position == size ){

return add(d);

}

// find node at index position-1

Node prev = head;

int count = 0;

while( count < position-1 ){

count += 1;

prev = prev.getNext();

} // prev will point to node before

Node n = new Node(d, prev.getNext() );

prev.setNext(n);

size += 1;

return this;

}

/* remove from the back */

public final String remove(){

if( tail == null || size == 0 ){ return null; }

String s = tail.get();

if( size == 1){

head = tail = null;

}else{

Node tmp = head;

for(int i=0; i<size-2; i+=1){

tmp = tmp.getNext();

} // at end of loop tmp.getNext() == tail is true

tail = tmp;

tail.setNext(null);

}

size -= 1;

return s;

}

/* remove first string in list */

public final String removeFront(){

if(head == null || size == 0){return null;}

String s = head.get();

if(size == 1){

head = tail = null;

}else{

Node tmp = head;

head = tmp.getNext();

tmp.setNext(null);

}

size -= 1;

return s;

}

/* add string to front of list */

public final ALinkedList addFront(String s){

if(size == 0){

head = tail = new Node(s, null);

}else{

head = new Node(s, head);

}

size += 1;

return this;

}

/* string representation of list */

@Override

public final String toString(){

String s = "[";

Node tmp = head;

for(int i=0; i<size-1; i++){

s += tmp.get() + ", ";

tmp = tmp.getNext();

}

if(size > 0){

s += tmp.get();

}

s += "]";

return s;

}

}

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