1. a)

    private static int sumOfFactors(int n) {
        int sum = 0;
        for (int i = 1; i < n; i++) {
            if (n % i == 0) {
                sum += i;
            }
        }
        return sum;
    }

1. b)
    
    private static boolean isPerfect(int n) {
        return (n == sumOfFactors(n));
    }

1. c)    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Please enter a positive integer");
        int n = scanner.nextInt();
        for (int i = 1; i <= n; i++) {
            if (isPerfect(i)) {
                System.out.println(i);
            }
        }
    }

1. d)

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Please enter a positive integer");
        int n = scanner.nextInt();
        for (int i = 1; i <= n; i++) {
            if (isPerfect(i)) {
                System.out.printf("%d = 1", i);
                for (int j = 2; j < i; j++) {
                    if (i % j == 0) {
                        System.out.printf(" + %d", j);
                    }
                }
                System.out.println();
            }
        }
    }

2.

public class TableTennis {
    private String playerOneName;
    private String playerTwoName;
    private int playerOneScore;
    private int playerTwoScore;
    private boolean deuce;
    
    public TableTennis(String playerOneName, String playerTwoName) {
        this.playerOneName = playerOneName;
        this.playerTwoName = playerTwoName;
        this.playerOneScore = 0;
        this.playerTwoScore = 0;
        this.deuce = false;
    }
    
    public String getPlayerOneName() {
        return this.playerOneName;
    }
    
    public String getPlayerTwoName() {
        return this.playerTwoName;
    }
    
    public int getPlayerOneScore() {
        return this.playerOneScore;
    }
    
    public int getPlayerTwoScore() {
        return this.playerTwoScore;
    }
    
    public void scoreOne() {
        this.playerOneScore++;
        if (this.playerOneScore == 10 && this.playerTwoScore == 10) {
            this.deuce = true;
        }
    }

    public void scoreTwo() {
        this.playerTwoScore++;
        if (this.playerOneScore == 10 && this.playerTwoScore == 10) {
            this.deuce = true;
        }
    }
    
    @Override
    public String toString() {
        return String.format("%s: %2d %s: %2d", this.playerOneName, this.playerOneScore, this.playerTwoName, this.playerTwoScore);
    }
    
    public int winner() {
        if (!this.deuce && this.playerOneScore > 10) {
            return 1;
        }
        if (!this.deuce && this.playerTwoScore > 10) {
            return 2;
        }
        if (this.deuce && this.playerOneScore >= this.playerTwoScore + 2) {
            return 1;
        }
        if (this.deuce && this.playerTwoScore >= this.playerOneScore + 2) {
            return 2;
        }
        return 0;
    }
}

3. Change the midPoint method to:

public Point midPoint(Point p) {
  double x = (this.x + p.x) / 2;
  double y = (this.y + p.y) / 2;
  return new Point(x, y);
}

4. A slow solution:

   public int missingElement(int[] a) {
        for (int i = 1; i <= 100; i++) {
            if (isMissing(a, i)) {
                return i;
            }
        }
    }

    private boolean isMissing(int[] a, int i) {
        for (int j : a) {
            if (j == i) {
                return false;
            }
        }
        return true;
    }

A fast solution:

    public int missingElement(int[] a) {
        int sum = 0;
        for (int j : a) {
            sum += j;
        }
        return 5050 - sum;
    }