EXAM Computer Science 1 Part 1

Transcription

1 Maastricht University Faculty of Humanities and Science Department of Knowledge Engineering EXAM Computer Science 1 Part 1 Block 1.1: Computer Science 1 Code: KEN1120 Examiner: Kurt Driessens Date: Januari 31, 2012 Time: 14h00 17h00 Place: Exam Notes: 1. The exam consists of two parts: The first part is closed book and should take about 30 minutes The second part is open book. You can use the Java Concepts book, printed slides and your own notes. 2. The time available for the entire exam (Part 1 and Part 2) is 180 minutes. 3. After handing in this first part and getting your book and notes out, you will receive the second part. 4. This first part consists of 4 pages (including this page). 5. The number of exam questions on the first part is For this part, fill out your answers on the question pages. 7. Please don t forget to write your name and student number on each page 1

2 Question 1 (12 points): Arrays in Java cannot change size once created. This causes problems when the number of elements to be stored is not known at creation time. Give multiple solutions and discuss their benefits and drawbacks. (Pay attention: using Java utilities such as ArrayLists that can change size after creation is not the answer I m looking for.) 2

3 Question 2 (5 points): What does pass-by-value mean? In which context is the term used? Question 3 (5 points): Why would you use the long type instead of the int type for variables? Question 4 (5 points): What is type casting or narrowing? How do you do this is Java? Question 5 (5 points): What is the edit-compile-test loop? 3

4 Question 6 (8 points): The following code is supposed to count the number of even values of an integer array. Correct all syntax and logical errors. The following code defines a class BankAccount. It remembers the balance of the account, defines a constructor, and methods to deposit and withdraw money from the account. Correct all syntax and logical errors. When finished, hand in this part to receive part 2 of the exam. 4

5 Maastricht University Faculty of Humanities and Science Department of Knowledge Engineering EXAM Computer Science 1 Part 2 Block 1.1: Computer Science 1 Code: KEN1120 Examiner: Kurt Driessens Date: Januari 31, 2012 Time: 14h00 17h00 Place: Exam Notes: 1. The time available for the entire exam (Part 1 and Part 2) is 180 minutes. 2. This second part consists of 3 pages (including this page). 3. There are 4 programming tasks in this second part. 4. Please don t forget: to write your name and student number on each page to number the pages to number the answers to mark which pages are scrap and which are not 5. After the exam hand in the exam questions and your scrap paper as well. 6. Try to structure your code and add comments even when you think your code is easy enough to understand. 5

6 Context: Sudoku is a number puzzle that consists of 81 spaces in a 9 by 9 arrangement that has to be filled with the digits 1,2,3,4,5,6,7,8 and 9 according to a few rules. These rules are: 1. Every digit appears once in each row. 2. Every digit appears once in each column. 3. Every digit appears once in each of the 9 3-by-3 sub-squares indicated on the puzzle (see below). Each Sudoku puzzle is made different by filling in an amount of starting digits. An example of a Sudoku puzzle is shown below on the left. A standard way of solving such a Sudoku puzzle is to write in each square, all digits that can still be placed in that square. We will call these collections of digits hints. See above on the right for an example. Then, the strategy to solve the Sudoku is to select the square with the least number of leftover possible digits and fill in the first possible value. The computation of the hints for all empty squares is then repeated. When a square is discovered with no possible digits, the puzzle can no longer be solved. This means filled in values must be erased up to the point where the selected square had other digits that could fit. 6

7 Your task is to implement 4 methods for an automated Sudoku solver. 1. (8 points) Write a method to see if a board still has empty squares to fill. The input of the method is a 9-by-9 integer array that represents the current board. Already filled in digits are stored in the array, while empty squares are represented by the value 0. The first index points to the row of the square, the second index to the column. The output of the method is a boolean that is true when the board is full and false when it is not. public boolean isfull (int[][] board) { 2. (25 points) Write a method that computes which digits are still available for a given square. The inputs of the method consist of the location of the square, i.e. the row and the column and a 9-by-9 integer array that represents the current board as described above. The output of the method should be a boolean array of length 10, in which the value at index is true if the digit index can still be used for the square and false otherwise. The value of the resulting array at index 0 does not matter. public boolean[] computehints (int row, int col, int[][] board) { 3. (12 points) Write a method that translates the boolean array that is the results of task 2 into an integer array that contains only the digits still available. This also means that the length of the resulting integer array should represent the number of available digits. public int[] collectdigits (boolean[] hints) { 4. (15 points) Write a method that returns the row and column of the best next square to fill in. In case there are multiple options, the method should pick one of them. You can call the methods from task 1, 2 and 3 to accomplish this task. The resulting array should contain 2 elements, the first one being the row and the second the column of the best next square. If there is a square with no more possibilities, the array should contain no elements, i.e. be of length 0. public int[] bestnextsquare (int[][] board) { 7