Duration: 90 minutes University Carlos III of Madrid Instructions for the exam: Books and notes are not allowed. Please write your name, surname, NIA and group on all pages. Problem 1 (2.5 points) Context: We have a simple linked list, implemented by MyLinkedList and Node classes: public class MyLinkedList { private Node first; private int numelems; MyLinkedList (){ first=null; numelems=0; public int getsize(){return numelems; public Object retrieventh (int pos){ // To implement public int insertnth (Object o, int pos){ // To implement public class Node { private Object info; private Node next; Node (Object obj) {info=obj; next=null; public void setinfo(object obj){ info=obj; public void setnext(node n){ next=n; public Object getinfo() {return info; public Node getnext(){return next; Section 1 (1.25 points) Implement the method public Object retrieventh (int pos) 1
from MyLinkedList class. This method returns the element placed at the pos -th position. If the position specified does not exist in the list (i.e. the position is out of bounds), the method must return null. Positions start at index 1. The method must not delete any item from the list. Section 2 (1.25 points) Implement the method public int insertnth (Object obj, int pos) from MyLinkedList class. This method takes as parameters both the object to be inserted and the position at which the object will be inserted. Positions start at index 1. Inserting an object at a specific position means that this object must be placed at that position. It might be necessary to shift other elements. For example, if there is an object to be inserted at position 3, then the element that was at position 3 before the insertion will be shifted to position 4. If the position specified is higher than the number of elements in the list, the object must be added at the end of the list (e.g. if the list contains 4 elements, and the position at which the new element is wanted to be added is 10, then the new element will be actually inserted at position 5). If the position specified is 0 or lower than 0, then no insertion must be done. The method must return the position at which the new element is finally inserted (the case in which pos>list size must be taken into account), or -1 is no insertion is made. Problem 2 (2.5 points) Context: We have a binary search tree representing a library (Library class). Each tree node stores information about a book: title, author and ISBN code. The tree is sorted alphabetically by book title in increasing order. We can assume there will not be two books with the same title. The following code implements the library: 2
public class Library { BNode root; public boolean insertbook(book con){ if (root==null) { root=new BNode(con); return true; else { return root.insertbook(con); public int getnumbooks (){ if (root==null) return 0; else return root.getnumbooks(); public class Book{ String title; String author; String isbn; Contact (){ title=""; author=""; isbn=""; public String gettitle() {return title; public String getauthor() {return author; public String getisbn() { return isbn; public class BNode { private Book info; private BNode left; private BNode right; public void setleft(bnode n) {left=n; public void setright(bnode n) {right=n; public BNode getright() {return right; public BNode getleft() {return left; public Book getinfo() {return info; public void setinfo(book c){ info = c; BNode (Book con) { setinfo(con); setleft(null); setright(null); public int getnumbooks(){ // // TO IMPLEMENT IN SECTION 1 public boolean insertbook(book con){ // // TO IMPLEMENT IN SECTION 2 3
Section 1 (1.25 points) Implement the method getnumbooks from BNode class. This method returns the number of books in the subtree which root node is the one invoking the method. Notice this method is the one called from getnumbooks method, from Library class, in order to get the total number of books in the library. This method must be solved recursively. Section 2 (1.25 points) Implement the method insertbook from BNode class. This method inserts the book (Book) specified as parameter at its corresponding place. Notice this method is the one called from the method insertbook from Library class. The method must return true if the book is inserted in the tree, or false if the book is not inserted because there is another book with the same title in the tree. This method must be solved recursively. 4
SOLUCIONES PROBLEMA 1 public Object retrieventh (int pos){ Node aux=first; if (pos<=0) return null; if (pos>getsize()) return null; for (int i=1;i<pos;i++){ aux=aux.getnext(); return aux.getinfo(); public int insertnth (Object o, int pos){ Node aux=first; Node newnode=new Node(o); if (pos<=0){ return -1; if (pos==1) { newnode.setnext(first); first=newnode; numelems++; else { if (pos>getsize()){ pos=getsize()+1; for (int i=1;i<pos-1;i++){ aux=aux.getnext(); newnode.setnext(aux.getnext()); aux.setnext(newnode); numelems++; return pos; Criterios de calificación Problema 1 Apartado 1) 0,75 puntos - Recorrer correctamente la lista hasta la posición requerida. Si la indexación no la hace correctamente desde 1, sino desde 0, se le da 0,5 puntos. 0,25 puntos - Check correcto de índice de posición fuera de rangos. 0,25 puntos - Return correcto del objeto. Apartado 2) 0,10 puntos. Crear correctamente el nodo a insertar. 0,25 puntos. Insertar correctamente en la primera posición. 0,25 puntos, recorrer hasta la posición a insertar. 0,25 puntos. Insertar correctamente en la posición nth. 5
0,15 controlar que la posición requerida sea mayor que el tamaño de la lista. 0,25 devolver correctamente la posición final. SOLUCIONES PROBLEMA 2 public int getnumbooks (){ int n=1; if (this.getleft()!=null){ n+=this.getleft().getnumbooks(); if (this.getright()!=null){ n+=this.getright().getnumbooks(); return n; public boolean insertbook(book newcon){ boolean res=false; int comp = this.getinfo().getname().compareto(newcon.getname()); if (comp == 0) { res=false; else if (comp < 0){ if (this.getright()==null) { this.setright(new BNode(newcon)); res=true; else{ res = this.getright().insertbook(newcon); else if (comp > 0){ if (this.getleft()==null) { this.setleft(new BNode(newcon)); res=true; else { res = this.getleft().insertbook(newcon); return res; Criterios de calificación Apartado 1) 0,25 Sumar correctamente 1 por el nodo actual. 0,25 Comprobar correctamente que las ramas!= null antes de invocar. 0,25 Invocar correctamente de forma recursiva. 0,25 sumar correctamente los return de las ramas. 0,25 devolver suma completa. Apartado 2) 0,15 Comparación correcta del título. 0,25 Comprobación de si es el título del nodo actual. 0,25 Comprobar si la rama correspondiente es null o no. 6
0,25 Insertar si la rama es null. 0,25 Invocar correctamente la llamada recursiva si la rama no es null. 0,10 return correcto de true/false. 7