hi, please help, thanks, see.question below, please post working code with outpu

Question

hi, please help, thanks, see.question below, please post working code with output:

Write a recursive method called "occur" that takes two arguments: a linked list of integers L and an integer N. It should return the Boolean true if N occurs in the list L, otherwise false. If L is null the answer must be false. If not, compare N to L.item. If they are equal, the answer is yes. If not, find the answer by calling the same function on the tail of L. Your main method should create a list L with members 1,2,3,4,5 and call the "occur" method twice: once to check if 4 occurs in the list L, and once to check if 9 occurs. Print both results.

Explanation / Answer

public class UnorderedLinkedList extends LinkedListClass { public UnorderedLinkedList() { super(); } public UnorderedLinkedList(UnorderedLinkedList otherList) { super(otherList); } //Method to determine whether searchItem is in //the list. //Postcondition: Returns true if searchItem is found // in the list; false otherwise. public boolean search(DataElement searchItem) { LinkedListNode current; //variable to traverse the list boolean found; current = first; //set current to point to the first //node in the list found = false; //set found to false while(current != null && !found) //search the list if(current.info.equals(searchItem)) //item is found found = true; else current = current.link; //make current point to //the next node return found; } //Method to delete deleteItem from the list. //Postcondition: If found, the node containing // deleteItem is deleted from the // list. Also first points to the first // node, last points to the last // node of the updated list, and count // is decremented by 1. public void deleteNode(DataElement deleteItem) { LinkedListNode current; //variable to traverse the list LinkedListNode trailCurrent; //variable just before current boolean found; if(first == null) //Case 1; the list is empty System.err.println("Cannot delete from an empty list."); else { if(first.info.equals(deleteItem)) //Case 2 { first = first.link; if(first == null) //the list had only one node last = null; count--; } else //search the list for the node with the given info { found = false; trailCurrent = first; //set trailCurrent to point to //the first node current = first.link; //set current to point to the //second node while(current != null && !found) { if(current.info.equals(deleteItem)) found = true; else { trailCurrent = current; current = current.link; } }//end while if(found) //Case 3; if found, delete the node { count--; trailCurrent.link = current.link; if(last == current) //node to be deleted was //the last node last = trailCurrent; //update the value of last } else System.out.println("Item to be deleted is " + "not in the list."); }//end else }//end else }//end deleteNode } public abstract class LinkedListClass { protected class LinkedListNode { DataElement info; LinkedListNode link; } protected LinkedListNode first; //variable to store the //address of the first //node of the list protected LinkedListNode last; //variable to store the //address of the last //node of the list protected int count; //variable to store the number of nodes //in the list //default constructor //Initializes the list to an empty state. //Postcondition: first = null, last = null, // count = 0 public LinkedListClass() { first = null; last = null; count = 0; } //Method to determine whether the list is empty. //Postcondition: Returns true if the list is empty; // false otherwise. public boolean isEmptyList() { return (first == null); } //Method to initialize the list to an empty state. //Postcondition: first = null, last = null, // count = 0 public void initializeList() { first = null; last = null; count = 0; } //Method to output the data contained in each node. public void print() { LinkedListNode current; //variable to traverse the list current = first; //set current so that it points to //the first node while(current != null) //while more data to print { System.out.print(current.info + " "); current = current.link; } }//end print //Method to return the number of nodes in the list. //Postcondition: The value of count is returned. public int length() { return count; } //Method to return a reference of the object containing //the data of the first node of the list. //Precondition: The list must exist and must not be empty. //Postcondition: The reference of the object that // contains the info of the first node // is returned. public DataElement front() { DataElement temp = first.info.getCopy(); return temp; } //Method to return a reference of object containing //the data of the last node of the list. //Precondition: The list must exist and must not be empty. //Postcondition: The reference of the object that // contains the info of the last node // is returned. public DataElement back() { DataElement temp = last.info.getCopy(); return temp; } //Method to determine whether searchItem is in the list. //Postcondition: Returns true if searchItem is found // in the list; false otherwise. public abstract boolean search(DataElement searchItem); //Method to insert newItem in the list. //Postcondition: first points to the new list // and newItem is inserted at the // beginning of the list. Also, // last points to the last node and // count is incremented by 1. public void insertFirst(DataElement newItem) { LinkedListNode newNode; //variable to create the //new node newNode = new LinkedListNode(); //create the new node newNode.info = newItem.getCopy(); //assign a copy of //newItem to the node newNode.link = first; //insert newNode before first first = newNode; //make first point to the //actual first node if(last == null) //if the list was empty, newNode is //also the last node in the list last = newNode; count++; } //Method to insert newItem at the end of the list. //Postcondition: first points to the new list and // newItem is inserted at the end // of the list. Also, last points to // the last node and // count is incremented by 1. public void insertLast(DataElement newItem) { LinkedListNode newNode; //variable to create the new node newNode = new LinkedListNode(); //create the new node newNode.info = newItem.getCopy(); //assign a copy of //newItem to the node newNode.link = null; //set the link field of //newNode to null if(first == null) //if the list is empty, newNode is //both the first and last node { first = newNode; last = newNode; } else //if the list is not empty, insert newNode after last { last.link = newNode; //insert newNode after last last = newNode; //set last to point to the actual last node } count++; }//end insertLast //Method to delete deleteItem from the list. //Postcondition: If found, the node containing // deleteItem is deleted from the // list. Also first points to the first // node, last points to the last // node of the updated list, and count // is decremented by 1. public abstract void deleteNode(DataElement deleteItem); //Method to return a reference of the copy of otherList. private void copy(LinkedListClass otherList) { LinkedListNode newNode; //variable to create a node LinkedListNode current; //variable to traverse the list first = null; //make this list empty if(otherList.first == null) //otherList is empty { first = null; last = null; count = 0; } else { count = otherList.count; current = otherList.first; //current points to the //list to be copied //copy the first element first = new LinkedListNode(); //create the node first.info = current.info.getCopy(); //copy the info first.link = null; //set the link field of //the node to null last = first; //make last point to the first node current = current.link; //make current point to the next //node of the list being copied //copy the remaining list while(current != null) { newNode = new LinkedListNode(); newNode.info = current.info.getCopy(); newNode.link = null; last.link = newNode; last = newNode; current = current.link; }//end while }//end else }//end copy //Method to return a reference of the copy of otherList. public void copyList(LinkedListClass otherList) { if(this != otherList) //avoid self-copy copy(otherList); } //copy constructor public LinkedListClass(LinkedListClass otherList) { copy(otherList); }//end copy constructor }

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