AP Computer Science Practice Test 4 - ArrayList and Sorting

Transcription

1 AP Computer Science Practice Test 4 - ArrayList and Sorting Name Date Period On multiple choice questions, choose the best answer. 1) Describe the action on the ArrayList (or array) elements through the larger for loop of the Selection SORT ) Describe the action on the ArrayList (or array) elements for the Merge SORT. YIPPEE BREAK IS ALMOST HERE AND CANNOT WAIT FOR IT 1

2 3) Assume that an ArrayList of String values has been declared as follows and has been initialized: ArrayList<String> names = new ArrayList<String>(); The ArrayList has more than two elements. Determine which of the following code segments correctly swaps the values contained at the first and last indices. I. II. III. (A) (B) (C) (D) (E) int last = names.size() - 1; String temp = names.get(last); names.remove(last); names.add(names.get(0)); names.remove(0); names.add(0, temp); String s1 = names.get(0); String s2 = names.get(names.size()-1); names.set(0, s2); names.set(names.size()-1, s1); int last = names.size() - 1; String n1 = names.get(0); names.remove(0); names.add(0, names.get(last)); names.add(n1); I only I and II only II only II and III only I, II, and III 4) Consider the following code fragment. int [][] arr = 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12, 13,14,15,16,17,18 ; for (int [] list : arr) for (int x : list) if (x % 4 == 2 && x % 3 == 0) System.out.print(x + ""); How many elements are printed? (A) 0 (B) 1 (C) 2 (D) 3 (E) 5 2

3 5) True or False a. Java always initializes arrays with default values. b. The size of an array is immutable. c. One of the features of an ArrayList is it can hold objects of multiple data types. d. The compareto() method returns a positive value if this is less than other. e. Insertion sorting will take, in the best case, n - 1 comparisons where n is the number of elements. f. Quadratic sorts are some of the most efficient sorts available. 6) Consider the following two methods: public static void somesort (int [] array) for (int i = 0; i < array.length - 1; i++) int j = indexsmallest(array, i, array.length - 1); int temp = array[i]; array[i] = array[j]; array[j] = temp; public static int indexsmallest (int[] array, int lower, int upper) int indexmin = lower; for (int i = lower + 1; i <= upper; i++) if (array[i] < array[indexmin]) indexmin = i; return indexmin; The sorting algorithm implemented in the somesort method can best be described as: (A) a Bubble Sort variation (B) a Selection Sort variation (C) an Insertion Sort variation (D) a Merge Sort variation (E) Does not sort the array 3

4 7) Consider the following incomplete method. Method findnext is intended to return the index of the first occurrence of the value val beyond the position start in ArrayList arr. You may not assume that such an occurrence always exists. // returns index of first occurrence of val in arr after position start; // returns arr.size() if val is not found public int findnext (ArrayList<Integer> arr, int val, int start) int pos = start + 1; while ( /* condition */ ) pos++; return pos; For example, consider the following code segment. ArrayList<Integer> array = new ArrayList<Integer>(Arrays.asList(11, 22, 100, 33, 55, 92, 100, 11, 44, 100, 76)); System.out.println(findNext(array,100,2)); The execution of the code segment should result in the value 6 being printed. Which of the following expressions could be used to replace /* condition */ so that findnext will work as intended? (A) (pos < arr.size()) (arr.get(pos)!= val) (B) (arr.get(pos) == val) && (pos < arr.size()) (C) (pos < arr.size()) (arr.get(pos) == val) (D) (pos < arr.size()) && (arr.get(pos)!= val) (E) (arr.get(pos)!= val) && (pos < arr.size()) 8) The following incomplete method is intended to sort its array parameter list in increasing order. public void sortthis(int [] list) int n = list.length; while ( n >= 2 ) int z = 0; for ( /* missing code */ ) if (list[i] > list[z]) z = i; int temp = list[n-1]; list[n-1] = list[z]; list[z] = temp; n--; Which of the following could be used to replace /* missing code */ so that executing the code segment sorts the values in array list? (A) int i = 0; i < n; i++ (D) int i = n; i > 0; i-- (B) int i = 1; i < n; i++ (E) int i = n - 1; i > 0; i-- (C) int i = 0; i < n - 1; i++ 4

5 9) Consider the following class definitions. public class ClassTwo extends ClassOne public void methodtwo ( ) public class ClassOne public void methodone ( ) public void methodtwo ( ) Now, consider the following declarations in a client class. You may assume that ClassOne and ClassTwo have default constructors. ClassOne c1 = new ClassOne(); ClassOne c2 = new ClassTwo(); Which of the following method calls will cause an error? I. c1.methodtwo(); II. c1.methodone(); III. c2.methodone(); (A) I only (B) II only (C) III only (D) I and II only (E) None of these will cause an error 10) Consider the following method, issorted, which is intended to return true if an array of ints is sorted in nondecreasing order and to return false otherwise. public static boolean issorted (int [] data) /* missing code */ Which of the following can be used to replace /* missing code */ so that issorted will work as intended? I. for (int k = data.length-2; k >= 0; k--) II. for (int k = data.length-1; k > 0; k--) if (data[k] > data[k + 1]) if (data[k - 1] > data[k]) return false; return false; return true; return true; III. for (int k = 0; k < data.length-1; k++) if (data[k] > data[k + 1]) return false; else return true; return true; (A) I only (B) II only (C) III only (D) I and II only (E) I and III only 5

6 11) Consider the following three methods that appear within a single class. public void methodtomadness ( ) ArrayList<Integer> nums = new ArrayList<Integer>(Arrays.asList(5, 4, 3, 2, 1)); newvalues(nums); for(int k = 0; k < nums.size(); k++) System.out.print(nums.get(k).intValue() + " "); mixthemup(nums); for(int k = 0; k < nums.size(); k++) System.out.print(nums.get(k).intValue() + " "); public void newvalues (ArrayList<Integer> list) for(int x = 0; x < list.size(); x++) list.set(x,new Integer(x * 2)); public void mixthemup (ArrayList<Integer> list) list = new ArrayList<Integer>(); for(int x = 0; x < 5; x++) list.add(new Integer(x * 5)); What is printed as a result of the call methodtomadness ()? (A) (B) (C) (D) (E) ) Which of the following declarations will cause an error? I. ArrayList<String> stringlist = new ArrayList<String>(); II. ArrayList<int> intlist = new ArrayList<int>(); III. ArrayList<Comparable> complist = new ArrayList<Comparable>(); (A) I only (B) II only (C) III only (D) I and III only (E) II and III only 6

7 13) Determine what will be printed from the following code fragment: ArrayList<String> mylist = new ArrayList<String>(); mylist.add("m"); mylist.add("v"); mylist.add("a"); mylist.add("p"); // Printed: mylist.add("c"); mylist.add("s"); for (int count = 0; count < mylist.size(); count+=2) mylist.remove(count); for (int count = 1; count <= mylist.size()/2; count++) mylist.add(1,"rain!"); for (String value : mylist) System.out.print(value + " "); 14) Determine what will be printed from the following code fragment: ArrayList<Integer> list = new ArrayList<Integer>(); list.add(3); list.add(2); list.add(1); // Printed: int n = list.size(); for (int i = 0; i < n; i++) int value = list.get(i); if (value > 0) list.add(value, new Integer(value)); System.out.println(list); 7

8 15) An organization raises money by selling boxes of cookies. A cookie order specifies the variety of cookie and the number of boxes ordered. The declaration of the CookieOrder class is shown below. public class CookieOrder /** Constructs a new CookieOrder object. */ public CookieOrder(String variety, int numboxes) /* implementation not shown */ the variety of cookie being ordered */ public String getvariety() /* implementation not shown */ the number of boxes being ordered */ public int getnumboxes() /* implementation not shown */ // There may be instance variables, constructors, and methods that are not shown. The MasterOrder class maintains a list of the cookies to be purchased. The declaration of the MasterOrder class is shown below. public class MasterOrder /** The list of all cookie orders */ private List<CookieOrder> orders; /** Constructs a new MasterOrder object. */ public MasterOrder() orders = new ArrayList<CookieOrder>(); /** Adds theorder to the master order. theorder the cookie order to add to the master order */ public void addorder(cookieorder theorder) orders.add(theorder); the sum of the number of boxes of all of the cookie orders */ public int gettotalboxes() /* to be implemented in part (a) */ /** Removes all cookie orders from the master order that have the same variety of * cookie as cookievar and returns the total number of boxes that were removed. cookievar the variety of cookies to remove from the master order the total number of boxes of cookievar in the cookie orders removed */ public int removevariety(string cookievar) /* to be implemented in part (b) */ // There may be instance variables, constructors, and methods that are not shown. 8

9 (a) The gettotalboxes method computes and returns the sum of the number of boxes of all cookie orders. If there are no cookie orders in the master order, the method returns 0. Complete method gettotalboxes below. the sum of the number of boxes of all of the cookie orders */ public int gettotalboxes() 9

10 (b) The removevariety method updates the master order by removing all of the cookie orders in which the variety of cookie matches the parameter cookievar. The master order may contain zero or more cookie orders with the same variety as cookievar. The method returns the total number of boxes removed from the master order. For example, consider the following code segment. MasterOrder goodies = new MasterOrder(); goodies.addorder(new CookieOrder("Chocolate Chip", 1)); goodies.addorder(new CookieOrder("Shortbread", 5)); goodies.addorder(new CookieOrder("Macaroon", 2)); goodies.addorder(new CookieOrder("Chocolate Chip", 3)); After the code segment has executed, the contents of the master order are as shown in the following table. Chocolate Chip 1 Shortbread 5 Macaroon 2 Chocolate Chip 3 The method call goodies.removevariety("chocolate Chip") returns 4 because there were two Chocolate Chip cookie orders totaling 4 boxes. The master order is modified as shown below. Shortbread 5 Macaroon 2 The method call goodies.removevariety("brownie") returns 0 and does not change the master order. Complete method removevariety below. /** Removes all cookie orders from the master order that have the same variety of * cookie as cookievar and returns the total number of boxes that were removed. cookievar the variety of cookies to remove from the master order the total number of boxes of cookievar in the cookie orders removed */ public int removevariety(string cookievar) 10