Add a method swapTwoNodes to SinglyLinkedList class from week 2 lecture examples. This method should swap two nodes node1 and node2 (and not just their contents) given references only to node1 and node2. The new method should check if node1 and node2 are the same node, etc. Write the main method to test the swapTwoNodes method. Hint: You may need to traverse the list.

* Copyright 2014, Michael T. Goodrich, Roberto Tamassia, Michael H. Goldwasser * * Developed for use with the book: * * Data Structures and Algorithms in Java, Sixth Edition * Michael T. Goodrich, Roberto Tamassia, and Michael H. Goldwasser * John Wiley & Sons, 2014 * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see . */ package linkedlists;

/** * A basic singly linked list implementation. * * @author Michael T. Goodrich * @author Roberto Tamassia * @author Michael H. Goldwasser */ public class SinglyLinkedList implements Cloneable { //---------------- nested Node class ---------------- /** * Node of a singly linked list, which stores a reference to its * element and to the subsequent node in the list (or null if this * is the last node). */ private static class Node {

/** The element stored at this node */ private E element; // reference to the element stored at this node

/** A reference to the subsequent node in the list */ private Node next; // reference to the subsequent node in the list

/** * Creates a node with the given element and next node. * * @param e the element to be stored * @param n reference to a node that should follow the new node */ public Node(E e, Node n) { element = e; next = n; }

// Accessor methods /** * Returns the element stored at the node. * @return the element stored at the node */ public E getElement() { return element; }

/** * Returns the node that follows this one (or null if no such node). * @return the following node */ public Node getNext() { return next; }

// Modifier methods /** * Sets the node's next reference to point to Node n. * @param n the node that should follow this one */ public void setNext(Node n) { next = n; } } //----------- end of nested Node class -----------

// instance variables of the SinglyLinkedList /** The head node of the list */ private Node head = null; // head node of the list (or null if empty)

/** The last node of the list */ private Node tail = null; // last node of the list (or null if empty)

/** Number of nodes in the list */ private int size = 0; // number of nodes in the list

/** Constructs an initially empty list. */ public SinglyLinkedList() { } // constructs an initially empty list

// access methods /** * Returns the number of elements in the linked list. * @return number of elements in the linked list */ public int size() { return size; }

/** * Tests whether the linked list is empty. * @return true if the linked list is empty, false otherwise */ public boolean isEmpty() { return size == 0; }

/** * Returns (but does not remove) the first element of the list * @return element at the front of the list (or null if empty) */ public E first() { // returns (but does not remove) the first element if (isEmpty()) return null; return head.getElement(); }

/** * Returns (but does not remove) the last element of the list. * @return element at the end of the list (or null if empty) */ public E last() { // returns (but does not remove) the last element if (isEmpty()) return null; return tail.getElement(); }

// update methods /** * Adds an element to the front of the list. * @param e the new element to add */ public void addFirst(E e) { // adds element e to the front of the list head = new Node<>(e, head); // create and link a new node if (size == 0) tail = head; // special case: new node becomes tail also size++; }

/** * Adds an element to the end of the list. * @param e the new element to add */ public void addLast(E e) { // adds element e to the end of the list Node newest = new Node<>(e, null); // node will eventually be the tail if (isEmpty()) head = newest; // special case: previously empty list else tail.setNext(newest); // new node after existing tail tail = newest; // new node becomes the tail size++; }

/** * Removes and returns the first element of the list. * @return the removed element (or null if empty) */ public E removeFirst() { // removes and returns the first element if (isEmpty()) return null; // nothing to remove E answer = head.getElement(); head = head.getNext(); // will become null if list had only one node size--; if (size == 0) tail = null; // special case as list is now empty return answer; }

@SuppressWarnings({"unchecked"}) public boolean equals(Object o) { if (o == null) return false; if (getClass() != o.getClass()) return false; SinglyLinkedList other = (SinglyLinkedList) o; // use nonparameterized type if (size != other.size) return false; Node walkA = head; // traverse the primary list Node walkB = other.head; // traverse the secondary list while (walkA != null) { if (!walkA.getElement().equals(walkB.getElement())) return false; //mismatch walkA = walkA.getNext(); walkB = walkB.getNext(); } return true; // if we reach this, everything matched successfully }

@SuppressWarnings({"unchecked"}) public SinglyLinkedList clone() throws CloneNotSupportedException { // always use inherited Object.clone() to create the initial copy SinglyLinkedList other = (SinglyLinkedList) super.clone(); // safe cast if (size > 0) { // we need independent chain of nodes other.head = new Node<>(head.getElement(), null); Node walk = head.getNext(); // walk through remainder of original list Node otherTail = other.head; // remember most recently created node while (walk != null) { // make a new node storing same element Node newest = new Node<>(walk.getElement(), null); otherTail.setNext(newest); // link previous node to this one otherTail = newest; walk = walk.getNext(); } } return other; }

public int hashCode() { int h = 0; for (Node walk=head; walk != null; walk = walk.getNext()) { h ^= walk.getElement().hashCode(); // bitwise exclusive-or with element's code h = (h << 5) | (h >>> 27); // 5-bit cyclic shift of composite code } return h; }

/** * Produces a string representation of the contents of the list. * This exists for debugging purposes only. */ public String toString() { StringBuilder sb = new StringBuilder("("); Node walk = head; while (walk != null) { sb.append(walk.getElement()); if (walk != tail) sb.append(", "); walk = walk.getNext(); } sb.append(")"); return sb.toString(); } //main method public static void main(String[] args) { SinglyLinkedList list = new SinglyLinkedList(); list.addFirst("MSP"); list.addLast("ATL"); list.addLast("BOS"); // list.addFirst("LAX"); System.out.println(list); // } }