APCS Study Guide Part I (Free Response)

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1 APCS Study Guide Part I (Free Response) Name: The final exam will have 2 free response questions on it. Use this review to develop your free response question skills. Feel free to write your answers on a separate sheet of paper so that you have more room. I also encourage you to code your solutions when you are finished in order to check your answers. Directions: SHOW ALL YOUR WORK. REMEMBER THAT PROGRAM SEGMENTS ARE TO BE WRITTEN IN JAVA. Notes: - Assume that the classes listed in the Quick Reference found in the Appendix have been imported where appropriate. - Unless otherwise noted in the question, assume that parameters in method calls are not null and that methods are called only when their preconditions are satisfied. - In writing solutions for each question, you may use any of the accessible methods that are listed in classes defined in that question. Writing significant amounts of code that can be replaced by a call to one of these methods may not receive full credit. Question #1: A statistician is studying sequences of numbers obtained by repeatedly tossing a six-sided number cube. On each side of the number cube is a single number in the range of 1 to 6, inclusive, and no number is repeated on the cube. The statistician is particularly interested in runs of numbers. A run occurs when two or more consecutive tosses of the cube produce the same value. For example, in the following sequence of cube tosses, there are runs starting at positions 1, 6, 12, and 14. Index Result The number cube is represented by the following class. public class NumberCube an integer value between 1 and 6, inclusive public int toss() /* implementation not shown You will implement a method that collects the results of several tosses of a number cube and another method that calculates the longest run found in a sequence of tosses.

2 (a) Write the method getcubetosses that takes a number cube and a number of tosses as parameters. The method should return an array of the values produced by tossing the number cube the given number of times. Complete method getcubetosses below. /** Returns an array of the values obtained by tossing a number cube numtosses times. cube a NumberCube numtosses the number of tosses to be recorded * Precondition: numtosses > 0 an array of numtosses values public static int[] getcubetosses(numbercube cube, int numtosses) (b) Write the method getlongestrun that takes as its parameter an array of integer values representing a series of number cube tosses. The method returns the starting index in the array of a run of maximum size. A run is defined as the repeated occurrence of the same value in two or more consecutive positions in the array. For example, the following array contains two runs of length 4, one starting at index 6 and another starting at index 14. The method may return either of those starting indexes. If there are no runs of any value, the method returns -1. Index Result Complete method getlongestrun below. /** Returns the starting index of a longest run of two or more consecutive repeated values * in the array values. values an array of integer values representing a series of number cube tosses * Precondition: values.length > 0 the starting index of a run of maximum size; * -1 if there is no run public static int getlongestrun(int[] values)

3 Question #2: The Chinese calendar associates an animal and an element with each year. There are 12 animals, associated with successive years, that rotate in a twelve-year cycle. The five elements, wood, fire, earth, metal, and water, combined with an elder or younger attribute, rotate in a ten-year cycle. The class ChineseZodiac below defines the names of the animals and the elements and provides static methods for determining the Zodiac description for a given year and for finding a year that matches the given animal and element: public class ChineseZodiac private static final int startyear = 1924; private static final String[] animals = rat, ox, tiger, rabbit, dragon, snake, horse, sheep, monkey, chicken, dog, pig private static final String[] elements = elder wood (fir), younger wood (bamboo), elder fire (burning wood), younger fire (lamp flame), elder earth (hill), younger earth (plain), elder metal (weapon), younger metal (kettle), elder water (wave), younger water (brook) ; //returns the zodiac string in the form // animal, element description that corresponds to year //precondition: year >= startyear public static String tozodiacstring(int year) /* to be implemented in part a The year startyear = 1924 was the year of the animal rat and the element fir as indicated by the values of animals[0] and elements[0]. The following year, 1925, was the year of the animal ox and the element bamboo as indicated by animals[1] and elements[1]. Note that in the past 60 years there were several years that were the year of the dragon but only one year that was both dragon and elder earth (hill).

4 A public class ChineseCalendar is a client of the ChineseZodiac class: public class ChineseCalendar //returns the zodiac string in the form // animal/informal element that corresponds to the year //precondition: year meets the precondition of the tozodiacstring method // of the ChineseZodiac class public String shortzodiac(int year) /* to be implemented in part b public int getyear(int year, String animal, String element) /* to be implemented in part c // constructors, other methods and instance variables // not shown (a) Write a method tozodiacstring of the ChineseZodiac class that returns a string that combines the animal name with the full element name for a given year, separated by a comma and a space. For example, tozodiacstring(1925) should return the string ox, younger wood (bamboo) Complete the method tozodiacstring below. // returns the zodiac string in the form // animal, element description that corresponds to year // precondition: year >= startyear public static String tozodiacstring(int year)

5 (b) Write a method shortzodiac of the class ChineseCalendar. shortzodiac returns a zodiac string for a given year in the colloquial format: a string that contains the animal name and the informal element name, removed from parentheses, separated by a slash character. For example, shortzodiac(1925) returns the string ox/bamboo Assume that tozodiacstring in the ChineseZodiac class works as specified, regardless of what you wrote in part (a). Complete method shortzodiac below. // returns the zodiac string in the form // animal/informal element that corresponds to year // precondition: year meets the precondition of the tozodiacstring method of the // ChineseZodiac class public String shortzodiac(int year) (c) Write a method getyear of the class ChineseCalendar. getyear returns the year of the first occurrence of a given animal and element (described by its full or informal name) since a specified year. For example, getyear(1924, ox, younger wood (bamboo) ) and getyear(1924, ox, bamboo ) both return The method should return 0 if either the animal or the element string is invalid. Assume that the methods described in parts (a) and (b) work as specified, regardless of what you wrote. Complete the method getyear below. //returns the year of the first occurrence of animal and //element in the Chinese calendar, since year //(year included); returns 0 if such year is not found //precondition: year meets the precondition of the // tozodiacstring method of the // ChineseZodiac class public int getyear(int year, String animal, String element)

6 Question #3: A game uses square tiles that have numbers on their sides. Each tile is labeled with a number on each of its four sides and may be rotated clockwise, as illustrated below. The tiles are represented by the NumberTile class, as given below. public class NumberTile /** Rotates the tile 90 degrees clockwise public void rotate() /* implementation not shown value at left edge of tile public int getleft() /* implementation not shown value at right edge of tile public int getright() /* implementation not shown Tiles are placed on a game board so that the adjoining sides of adjacent tiles have the same number. The following figure illustrates an arrangement of tiles and shows a new tile that is to be placed on the game board.

7 In its original orientation, the new tile can be inserted between the tiles at positions 2 and 3 or between the tiles at positions 3 and 4. If the new tile is rotated once, it can be inserted before the tile at position 0 (the first tile) or after the tile at position 4 (the last tile). Assume that the new tile, in its original orientation, is inserted between the tiles at positions 2 and 3. As a result of the insertion, the tiles at positions 3 and 4 are moved one location to the right, and the new tile is inserted at position 3, as shown below. A partial definition of the TileGame class is given below. public class TileGame /** represents the game board; guaranteed never to be null private ArrayList<NumberTile> board; public TileGame() board = new ArrayList<NumberTile>(); /** Determines where to insert tile, in its current orientation, into game board tile the tile to be placed on the game board the position of tile where tile is to be inserted: * 0 if the board is empty; * -1 if tile does not fit in front, at end, or between any existing tiles; * otherwise, 0 position returned board.size() private int getindexforfit(numbertile tile) /* to be implemented in part (a) /** Places tile on game board if it fits (checking all possible tile orientations if necessary). * If there are no tiles on the game board, the tile is placed at position 0. * The tile should be placed at most 1 time. * Precondition: board is not null tile the tile to be placed on the game board true if tile is placed successfully; false otherwise * Postcondition: the orientations of the other tiles on the board are not changed * Postcondition: the order of the other tiles on the board relative to each other is not changed public boolean inserttile(numbertile tile) /* to be implemented in part (b)

8 (a) Write the TileGame method getindexforfit that determines where a given tile, in its current orientation, fits on the game board. A tile can be inserted at either end of a game board or between two existing tiles if the side(s) of the new tile match the adjacent side(s) of the tile(s) currently on the game board. If there are no tiles on the game board, the position for the insert is 0. The method returns the position that the new tile will occupy on the game board after it has been inserted. If there are multiple possible positions for the tile, the method will return any one of them. If the given tile does not fit anywhere on the game board, the method returns -1. For example, the following diagram shows a game board and two potential tiles to be placed. The call getindexforfit(tile1) can return either 3 or 4 because tile1 can be inserted between the tiles at positions 2 and 3, or between the tiles at positions 3 and 4. The call getindexforfit(tile2) returns -1 because tile2, in its current orientation, does not fit anywhere on the game board. Complete method getindexforfit below. /** Determines where to insert tile, in its current orientation, into game board tile the tile to be placed on the game board the position of tile where tile is to be inserted: * 0 if the board is empty; * -1 if tile does not fit in front, at end, or between any existing tiles; * otherwise, 0 position returned board.size() private int getindexforfit(numbertile tile)

9 (b) Write the TileGame method inserttile that attempts to insert the given tile on the game board. The method returns true if the tile is inserted successfully and false only if the tile cannot be placed on the board in any orientation. Assume that getindexforfit works as specified, regardless of what you wrote in part (a). Complete method inserttile below. /** Places tile on the game board if it fits (checking all possible tile orientations if necessary). * If there are no tiles on the game board, the tile is placed at position 0. * The tile should be placed at most 1 time. * Precondition: board is not null tile the tile to be placed on the game board true if tile is placed successfully; false otherwise * Postcondition: the orientations of the other tiles on the board are not changed * Postcondition: the order of the other tiles on the board relative to each other is not changed public boolean inserttile(numbertile tile)

10 Question #4: A travel agency maintains a list of information about airline flights. Flight information includes a departure time and an arrival time. You may assume that the two times occur on the same day. These times are represented by objects of the Time class. The declaration for the Time class is shown below. It includes a method minutesuntil that returns the difference (in minutes) between the current Time object and another Time object. public class Time difference, in minutes, between this time and other; * difference is negative if other is earlier than this time public int minutesuntil(time other) /* implementation not shown For example, assume that t1 and t2 are Time objects where t1 represents 1:00 P.M. and t2 represents 2:15 P.M. The call t1.minutesuntil(t2) will return 75 and the call t2.minutesuntil(t1) will return -75. The declaration for the Flight class is shown below. It has methods to access the departure time and the arrival time of a flight. You may assume that the departure time of a flight is earlier than its arrival time. public class Flight time at which the flight departs public Time getdeparturetime() /* implementation not shown time at which the flight arrives public Time getarrivaltime() /* implementation not shown

11 A trip consists of a sequence of flights and is represented by the Trip class. The Trip class contains an ArrayList of Flight objects that are stored in chronological order. You may assume that for each flight after the first flight in the list, the departure time of the flight is later than the arrival time of the preceding flight in the list. A partial declaration of the Trip class is shown below. You will write two methods for the Trip class. public class Trip private ArrayList<Flight> flights; // stores the flights (if any) in chronological order the number of minutes from the departure of the first flight to the arrival * of the last flight if there are one or more flights in the trip; * 0, if there are no flights in the trip public int getduration() /* to be implemented in part (a) /** Precondition: the departure time for each flight is later than the arrival time of its * preceding flight the smallest number of minutes between the arrival of a flight and the departure * of the flight immediately after it, if there are two or more flights in the trip; * -1, if there are fewer than two flights in the trip public int getshortestlayover() /* to be implemented in part (b) (a) Complete method getduration below. the number of minutes from the departure of the first flight to the arrival * of the last flight if there are one or more flights in the trip; * 0, if there are no flights in the trip public int getduration()

(b) Write the Trip method getshortestlayover. A layover is the number of minutes from the arrival of one flight in a trip to the departure of the flight immediately after it.

12 (b) Write the Trip method getshortestlayover. A layover is the number of minutes from the arrival of one flight in a trip to the departure of the flight immediately after it. If there are two or more flights in the trip, the method should return the shortest layover of the trip; otherwise, it should return -1. For example, assume that the instance variable flights of a Trip object vacation contains the following flight information. The call vacation.getshortestlayover() should return 15. Complete method getshortestlayover below. /** Precondition: the departure time for each flight is later than the arrival time of its * preceding flight the smallest number of minutes between the arrival of a flight and the departure * of the flight immediately after it, if there are two or more flights in the trip; * -1, if there are fewer than two flights in the trip public int getshortestlayover()

13 Question #5: Consider a method of encoding and decoding words that is based on a master string. This master string will contain all the letters of the alphabet, some possibly more than once. An example of a master string is "sixtyzipperswerequicklypickedfromthewovenjutebag". This string and its indexes are shown below. An encoded string is defined by a list of string parts. A string part is defined by its starting index in the master string and its length. For example, the string "overeager" is encoded as the list of string parts [ (37, 3), (14, 2), (46, 2), (9, 2) ] denoting the substrings "ove", "re", "ag", and "er". String parts will be represented by the StringPart class shown below. public class StringPart start the starting position of the substring in a master string length the length of the substring in a master string public StringPart(int start, int length) /* implementation not shown the starting position of the substring in a master string public int getstart() /* implementation not shown the length of the substring in a master string public int getlength() /* implementation not shown

14 The class StringCoder provides methods to encode and decode words using a given master string. When encoding, there may be multiple matching string parts of the master string. The helper method findpart is provided to choose a string part within the master string that matches the beginning of a given string. public class StringCoder private String masterstring; master the master string for the StringCoder * Precondition: the master string contains all the letters of the alphabet public StringCoder(String master) masterstring = master; parts an ArrayList of string parts that are valid in the master string * Precondition: parts.size() > 0 the string obtained by concatenating the parts of the master string public String decodestring(arraylist<stringpart> parts) /* to be implemented in part (a) str the string to encode using the master string * Precondition: all of the characters in str appear in the master string; * str.length() > 0 a string part in the master string that matches the beginning of str. * The returned string part has length at least 1. private StringPart findpart(string str) /* implementation not shown word the string to be encoded * Precondition: all of the characters in word appear in the master string; * word.length() > 0 an ArrayList of string parts of the master string that can be combined * to create word public ArrayList<StringPart> encodestring(string word) /* to be implemented in part (b)

15 Write the StringCoder method decodestring. This method retrieves the substrings in the master string represented by each of the StringPart objects in parts, concatenates them in the order in which they appear in parts, and returns the result. Complete method decodestring below. parts an ArrayList of string parts that are valid in the master string * Precondition: parts.size() > 0 the string obtained by concatenating the parts of the master string public String decodestring(arraylist<stringpart> parts) Write the StringCoder method encodestring. A string is encoded by determining the substrings in the master string that can be combined to generate the given string. The encoding starts with a string part that matches the beginning of the word, followed by a string part that matches the beginning of the rest of the word, and so on. The string parts are returned in an array list in the order in which they appear in word. The helper method findpart must be used to choose matching string parts in the master string. Complete method encodestring below. word the string to be encoded * Precondition: all of the characters in word appear in the master string; * word.length() > 0 an ArrayList of string parts of the master string that can be combined * to create word public ArrayList<StringPart> encodestring(string word)

CS/ENGRD 2110 Object-Oriented Programming and Data Structures Spring 2012 Thorsten Joachims. Lecture 17: Heaps and Priority Queues

CS/ENGRD 2110 Object-Oriented Programming and Data Structures Spring 2012 Thorsten Joachims Lecture 17: Heaps and Priority Queues Stacks and Queues as Lists Stack (LIFO) implemented as list insert (i.e.