Uppgift 1)

a) [8, 11, 14]

b) false
true
false

c) The code swaps each pair of entries twice.  Change the loop bound to arr.length / 2.

d) The two backslashes need to be escaped, i.e. replaced with \\

Uppgift 2)

a)  public static boolean isPrime(int x) {
        if (x <= 1)
            return false;
        if (x % 2 == 0)
            return (x == 2);
        double squareRoot = Math.sqrt(x);
        for (int i = 3; i <= squareRoot; i++) {
            if (x % i == 0)
                return false;
        }
        return true;
    }
    
b)  public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enter a number");
        int x = keyboard.nextInt();
        while (x > 1) {
            // Find the largest prime factor of x
            for (int i = x; i > 1; i--) {
                if (isPrime(i) && x % i == 0) {
                    System.out.print(i);
                    System.out.print(" ");
                    x = x / i;
                    break;
                }
            }
        }
    }

Uppgift 3)

import java.util.*;
import java.io.*;

class Uppgift3{
  public static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzåäö";

  public static String encode(String text, int key){
    String plainTxt = text.toLowerCase();
    String cipher = "";
    for(int i = 0; i < plainTxt.length(); i++){
      int charPos = ALPHABET.indexOf(plainTxt.charAt(i));
      int keyVal = (key + charPos) % ALPHABET.length();
      char codeChar = ALPHABET.charAt(keyVal);
      cipher += codeChar;
    }
    return cipher;
  }

  public static void main(String[] args) {
    if (args.length != 3) {
          System.out.println("Felaktigt antal argument.");
          System.exit(0);
        }
    Scanner in = null;
    try{
      // Fil för indata.
      in = new Scanner(new File(args[0]));
     }
     catch(FileNotFoundException e){
      System.out.println(e.getMessage());
      System.exit(0);
    }
    PrintStream w = null;
    try{
      // Fil för utdata
    w = new PrintStream(new File(args[1]));
    }
    catch(FileNotFoundException e){
      System.out.println(e.getMessage());
      System.exit(0);
      }
      // Nyckel för kryptering.
    int key = Integer.parseInt(args[2]);

    while(in.hasNext()){
      String s = encode(in.next(),key);
      w.print(s + " ");
    }
    in.close();
    w.close();
  }
}

Uppgift 4)

import java.util.*;

public abstract class Gate {
  protected String name;

  public Gate(String name) {
    this.name = name;
  }

  public abstract boolean getOutput();
  
  public String getName() {
    return name;
  }
}

class ConstantGate extends Gate {

  private boolean value;

  public ConstantGate(String name) {
    super(name);
  }

  public void set(boolean v) {
    value = v;
  }

  public boolean getOutput() {
    return value;
  } 

}

abstract class BasicGate extends Gate {
  protected List<Gate> input = new ArrayList<Gate>();

  protected BasicGate(String name) {
    super(name);
  }

  protected void checkInput() {
    if (input.size() < 2)
      throw new IllegalStateException("Gate " + name + ": Input signal(s) missing");
  }    

  protected abstract boolean calculateValue();

  public void setInput(Gate g) {
    input.add(g);
  }

  public boolean getOutput() {
    checkInput();
    return calculateValue();
  }
}

class AndGate extends BasicGate {

  public AndGate(String name) {
    super(name);
  }

  protected boolean calculateValue() {
    for (Gate g : input)
      if (!g.getOutput())
        return false;
    return true;
  }
}

class OrGate extends BasicGate {

  public OrGate(String name) {
    super(name);
  }

  protected boolean calculateValue() {
    for (Gate g : input)
      if (g.getOutput())
        return true;
    return false;
  }
}

class NotGate extends BasicGate {

  protected NotGate(String name) {
    super(name);
  }

  @Override
  protected void checkInput() {
    if (input.size() != 1)
      throw new IllegalStateException("Gate " + name + ": Illegal number of input signals");
  } 

  protected boolean calculateValue() {
    return !input.get(0).getOutput();
  }
}

Uppgift 5)

public class Lines extends JPanel {
  private int n;

  public Lines(int n) {
    this.n = n;
  }

  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Insets i = getInsets(); 
    int w = getWidth()  - i.left-i.right;
    int h = getHeight() - i.top - i.bottom;
    int dx = w/(n+1);
    int dy = h/(n+1);
    for (int j = 1; j <= n; j++)
      g.drawLine(i.left+j*dx, i.top+h, i.left+w, i.top+h-j*dy);
  }
}

Uppgift 6)

import java.util.*; 
public class Airport {
  private String name;
  private NavigableSet<Flight> departures = new TreeSet<Flight>();
  private Map<String, NavigableSet<Flight>> flightsTo = new HashMap<String, NavigableSet<Flight>>();

  public Airport(String n) {
    name = n;
  }

  public String getName() {
    return name;
  }

  public NavigableSet<Flight> getDepartures() {
    return departures;
  }

  public NavigableSet<Flight> getDepartures(String to) {
    return flightsTo.get(to);
  }

  public void addFlight(Flight f) {
    departures.add(f);
    if (!flightsTo.containsKey(f.getDestination()))
      flightsTo.put(f.getDestination(), new TreeSet<Flight>());
    flightsTo.get(f.getDestination()).add(f); 
  }

  public void removeFlight(Flight f) {
      departures.remove(f);
      NavigableSet<Flight> e = flightsTo.get(f.getDestination());
      if (e != null) {
	e.remove(f);
	if (e.isEmpty())
	  flightsTo.remove(f.getDestination());
      }
  }           
}