C212 Fall 2010 Final Exam Answers

Transcription

1 C212 Fall 2010 Final Exam Answers 1. Here s my code: cat Profile.java class Profile { String input = args[0]; String memory = ""; for (int i = 0; i < input.length(); i++) { char c = input.charat(i); if (contains(memory, c) == 0) { System.out.println( c + " occurs " + contains(input, c) + " times " ); memory += input.charat(i); static int contains(string input, char c) { int count = 0; for (int i = 0; i < input.length(); i++) if (input.charat(i) == c) count += 1; return count; javac Profile.java java Profile banana b occurs 1 times a occurs 3 times n occurs 2 times

2 2. Here s my code: cat Second.java class Second { static void simplify(int a, int b) { int m = Math.min(Math.abs(a), Math.abs(b)); System.out.print(a + "/" + b + " = "); for (int i = 2; i < m; i++) while (a % i == 0 && b % i == 0) { a /= i; b /= i; System.out.println(a + "/" + b); Second.simplify(6, 9); Second.simplify(-4, 6); javac Second.java java Second 6/9 = 2/3-4/6 = -2/3

3 3. Here s my code: cat Fraction.java class Fraction { private int numerator; private int denominator; public Fraction(int num, int den) { if (den == 0) System.exit(0); if (num == 0) { num = 0; den = 1; else if (den < 0) { num *= -1; den *= -1; this.numerator = num; this.denominator = den; this.reduce(); void reduce() { int m = Math.min(Math.abs(this.numerator), Math.abs(this.denominator)); for (int i = 2; i <= m; i++) while (this.numerator % i == 0 && this.denominator % i == 0) { this.numerator /= i; this.denominator /= i; public String tostring() { String fraction; if (denominator == 1) { fraction = numerator + ""; else { fraction = numerator + "/" + denominator; if (denominator * numerator < 0) { return "(" + fraction + ")"; else { return fraction; public boolean iszero() { return (denominator == 1 && numerator == 0); public boolean isint() { return (denominator == 1); boolean equals(fraction other) { return (this.minus(other)).iszero(); boolean greaterthan(fraction other) { return (this.minus(other)).ispositive(); boolean ispositive() { return this.numerator * this.denominator > 0; public Fraction minus(fraction other) { return new Fraction( numerator * other.denominator - other.numerator * denominator, denominator * other.denominator ); public Fraction plus(fraction other) { return new Fraction( numerator * other.denominator + other.numerator * denominator, denominator * other.denominator ); public Fraction times(fraction other) { return new Fraction(numerator * other.numerator, denominator * other.denominator); public Fraction divideby(fraction other) { return new Fraction(numerator * other.denominator, denominator * other.numerator); // from here on what was given already: Fraction f = new Fraction(6, 9); Fraction g = new Fraction(-4, 6); System.out.println("Test of operations: "); System.out.println(" Add: " + f + " + " + g + " = " + f.plus(g));

4 System.out.println(" Sub: " + f + " - " + g + " = " + f.minus(g)); System.out.println(" Mul: " + f + " * " + g + " = " + f.times(g)); System.out.println(" Div: " + f + " / " + g + " = " + f.divideby(g)); System.out.println("Test of predicates: "); System.out.print(" 1. Does " + f + " equal " + g + "? "); System.out.println(" The answer is: " + f.equals(g)); Fraction h = new Fraction(8, -2); System.out.print(" 2. Is " + h + " an integer? "); System.out.println("The answer is: " + h.isint()); Fraction i, j; i = (f.minus(g)).times(f.plus(g)); j = f.times(f).minus(g.times(g)); System.out.print(" 3. Does " + i + " equal " + j + "? "); System.out.println("The answer is: " + i.equals(j)); System.out.print(" 4. Is 5/8 greater than 2/3? The answer is: "); System.out.println((new Fraction(5, 8)).greaterThan(new Fraction (2, 3))); javac Fraction.java java Fraction Test of operations: Add: 2/3 + (-2/3) = 0 Sub: 2/3 - (-2/3) = 4/3 Mul: 2/3 * (-2/3) = (-4/9) Div: 2/3 / (-2/3) = (-1) Test of predicates: 1. Does 2/3 equal (-2/3)? The answer is: false 2. Is (-4) an integer? The answer is: true 3. Does 0 equal 0? The answer is: true 4. Is 5/8 greater than 2/3? The answer is: false

5 4.1 Here s my code: cat Jugador 1.java class Jugador extends Player { Jugador(String name) { super(name); boolean iswinner() { return score() % 7 == 0; cat Juego 2.java import java.util.*; class Juego { ArrayList<Player> players = new ArrayList<Player>(); int n = Integer.parseInt(args[0]); for (int i = 0; i < n; i++) players.add(new Jugador("Player " + i)); Game a = new Game(players); a.start(); javac Juego.java java Juego 5 Player 0: [2] false Player 2: [6] false Player 3: [1] false Player 4: [3] false Player 0: [2, 1] false Player 1: [2, 5] true java Juego 5 Player 0: [6] false Player 2: [5] false Player 3: [3] false Player 4: [1] false Player 0: [6, 2] false Player 1: [2, 1] false Player 2: [5, 2] true java Juego 3 Player 0: [6] false Player 1: [1] false Player 2: [2] false Player 0: [6, 4] false Player 1: [1, 3] false Player 2: [2, 4] false Player 0: [6, 4, 3] false Player 1: [1, 3, 4] false Player 2: [2, 4, 5] false 1 Jugador means Player in Spanish. 2 Juego means Game in Spanish

6 Player 0: [6, 4, 3, 4] false Player 1: [1, 3, 4, 2] false Player 2: [2, 4, 5, 4] false Player 0: [6, 4, 3, 4, 5] false Player 1: [1, 3, 4, 2, 2] false Player 2: [2, 4, 5, 4, 6] true 4.2 Here s my code: cat Jatek.java import java.util.*; class Jatek 3 extends Game { Jatek(ArrayList<Player> players) { super(players); void start() { boolean gameon = true; while (gameon) { for (Player p : players) { p.add(d.shake()); if (p.iswinner()) gameon = false; System.out.println(p); ArrayList<Player> players = new ArrayList<Player>(); int n = Integer.parseInt(args[0]); for (int i = 0; i < n; i++) players.add(new Player("Player " + i)); Game a = new Jatek(players); a.start(); javac Jatek.java java Jatek 2 Player 0: [2] false Player 0: [2, 6] false Player 1: [2, 6] false Player 0: [2, 6, 6] false Player 1: [2, 6, 3] false Player 0: [2, 6, 6, 4] false Player 1: [2, 6, 3, 6] false Player 0: [2, 6, 6, 4, 4] true Player 1: [2, 6, 3, 6, 5] true java Jatek 3 Player 0: [5] false Player 2: [6] false Player 0: [5, 3] false Player 1: [2, 3] false Player 2: [6, 6] false Player 0: [5, 3, 1] false 3 Jatek means Game in Hungarian.

7 Player 1: [2, 3, 3] false Player 2: [6, 6, 4] false Player 0: [5, 3, 1, 4] false Player 1: [2, 3, 3, 5] false Player 2: [6, 6, 4, 2] false Player 0: [5, 3, 1, 4, 2] false Player 1: [2, 3, 3, 5, 5] false Player 2: [6, 6, 4, 2, 2] false Player 0: [5, 3, 1, 4, 2, 3] false Player 1: [2, 3, 3, 5, 5, 6] true Player 2: [6, 6, 4, 2, 2, 4] true