Computação I. Exercises. Leonardo Vanneschi NOVA IMS, Universidade Nova de Lisboa. Leonardo Vanneschi Computação I NOVA IMS

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1 Computação I Exercises Leonardo Vanneschi NOVA IMS, Universidade Nova de Lisboa 1

2 Exercise 1 Write a Java program composed by: a. A method called myaverage that has the following parameters: an array A of elements of type doubles, a variable n of type double and a boolean variable called flag. If flag is true the method must return the average of the elements in A that are divisible by n. If flag is false the method must return the average of the elements in A that are larger than n. a. A main method in which the program asks the user the number of elements of an array X. The program asks the user to enter the number of elements until the value is greater than 0. After calling the function myaverage with values decided by the user, the program will print in the main method the value returned by the method. 2

3 Solution of Exercise 1 import java.util.*; public class Exercise { static double myaverage (double[] A, double n, boolean flag) { double res = 0; if (flag) { int cont = 0; for (int i = 0; i < A.length; i++) { if (A[i] % n == 0) { cont++; res = res + A[i]; res = res/cont; else { int cont = 0; for (int i = 0; i < A.length; i++) { if (A[i] > n) { cont++; res = res + A[i]; res = res/cont; return res; 3

4 Solution of Exercise 1 (cont) public static void main(string[] args) { Scanner key = new Scanner(System.in); System.out.println("Write the size of the array (positive number)"); int N = key.nextint(); while (N <= 0) { System.out.println("The number was not positive, try again!"); N = key.nextint(); double[] vec = new double[n]; for (int i = 0; i < N; i++) { System.out.println("Write the element of index " + i); vec[i] = key.nextdouble(); key.close(); // closes main // closes class double result = myaverage(vec, 2, true); System.out.println("The result is: " + result); 4

5 Exercise 2 Write a Java program composed by: a. A method called diff that returns an array of elements of type double and that has two parameters: an array A of elements of type double and an array B of elements of type double. The method will return an array C that contains in each position C[i]: the difference between A[i] and B[i] if A[i] > B[i]. the difference between B[i] and A[i] in the opposite case. b. A main method in which the program asks the user the number of elements of two arrays X and Y of elements of type double (X and Y have the same size). The program asks the user to enter the number of elements until the value is greater than 0. Then, the user has to fill the arrays. The program will call the method diff passing as parameters X and Y and it will print on the console the elements of the array returned by diff. 5

6 Solution of Exercise 2 public class Exe2 { public static void main(string[] args) { // very similar to exercise 1 static double[] diff(double[] A, double[] B) { double[] C = new double[a.length]; for (int i = 0; i < C.length; i++) { if (A[i] > B[i]) { C[i] = A[i] - B[i]; else { C[i] = B[i] - A[i]; return C; 6

7 Exercise 3 1) Write a Java Program composed by: a. A method called visit that has as parameter an array A of elements of type int and returns a boolean value. Each element A[i] represents the index of the element of A that must be visited after visiting A[i]. The function returns true if, according to the information contained in A, all the elements of A are visited. The visit starts at the beginning of the array (index 0). The function returns false otherwise. b. A main method in which calls the method visit passing as parameter an array composed by the values passed by the user at the moment of the execution of the programs (args), after the appropriate transformation of type. In the main method the program will inform the user about the result of the visit of X by printing a message on the console (i.e. The visit of X has been completed or Impossible to visit all the elements of X ). 7

8 Example: In this case the method will return true because all the elements of the array are visited. In this case the method will return false because not all the elements of the array can be visited. 8

9 Solution of Exercise 3 public class Exerc3 { public static void main(string[] args) { int[] X = new int[args.length]; for (int i = 0; i < args.length; i++) { X[i] = Integer.parseInt(args[i]); boolean res = visit(x); if (res) { System.out.println("I have visited them all!"); else { System.out.println("It is IMPOSSIBLE to visit them all"); 9

10 static boolean visit (int[] A) { boolean[] alreadyvisited = new boolean[a.length]; for (int i = 0; i < A.length; i++) alreadyvisited[i] = false; int nextindex = 0; while (!alreadyvisited[nextindex]) { alreadyvisited[nextindex] = true; nextindex = A[nextIndex]; if (nextindex >= A.length) { System.out.println("The value " + nextindex + " is out of range"); System.exit(-1); boolean result = true; for (int i = 0; i < A.length; i++) { System.out.println("For element " + i + " the visit is: " + alreadyvisited[i]); if (!alreadyvisited[i]) { result = false; return result; // closes method visit // closes class 10

11 Exercise 4 Write a Java program composed by the following methods: a) A method called integerroot that has as parameter an integer K and returns an integer value representing the integer square root of K. The integer square root of K is defined as the biggest integer number S such that S*S<=K. This method can assume that K is a positive number, without any further control. b) A method arrayroot that has as parameter an array A of elements of type int. The method returns an array B that contains, in each position B[i], the integer square root of the corresponding element A[i]. c) The main method that calls the method arrayroot by passing as parameter a vector composed by the values passed by the user at the moment of the execution of the program (args), after the appropriate transformation of type. The main method must display an error message if at least one of the elements of the argument array is not positive, and the elements of the array returned by arrayroot otherwise. 11

12 Solution of Exercise 4 public class Exe4 { public static void main(string[] args) { int[] argsint = new int[args.length]; for (int i = 0; i < args.length; i++) { argsint[i] = Integer.parseInt(args[i]); if (argsint[i] < 0) { System.out.println("Error: the number " + argsint[i] + " is negative!"); System.exit(-1); int[] B = arrayroot(argsint); System.out.println("Integer roots:"); for (int i = 0; i < B.length; i++) { System.out.print(B[i] + "\t"); System.out.println(); 12

13 Solution of Exercise 4 (cont.) static int integerroot (int K) { int S = 0; for (int i = 0; i < K; i++) { if (i*i <= K) { S = i; return S; static int[] arrayroot (int[] A) { int[] B = new int[a.length]; for (int i = 0; i < A.length; i++) { B[i] = integerroot(a[i]); return B; // closes the class 13