2019 FRQ 4

Part A

class LightBoard
{

    private boolean[][] lights;

    public LightBoard(int numRows, int numCols)
    {
        lights = new boolean[numRows][numCols];
        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j < numCols; j++) {
                lights[i][j] = (Math.random() < 0.4);
            }
        }
    }

    public boolean evaluateLight(int row, int col)
    { return false; }

    public void printBoard() {
        for (int r = 0; r < lights.length; r++) {
            for (int c = 0; c < lights[0].length; c++) {
                System.out.print((lights[r][c] ? "T" : "F") + " ");
            }
            System.out.println();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        LightBoard board = new LightBoard(5, 5);
        System.out.println("Part A - Initial Board (T = true/on, F = false/off):");
        board.printBoard();
    }
}

Main.main(null)

Part A - Initial Board (T = true/on, F = false/off):
F F T F F 
T T F F T 
F F F T F 
F F T T F 
T F T F F 

Part B

class LightBoard
{

    private boolean[][] lights;

    public LightBoard(int numRows, int numCols)
    {
        lights = new boolean[numRows][numCols];
        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j < numCols; j++) {
                lights[i][j] = (Math.random() < 0.4);
            }
        }
    }

    public boolean evaluateLight(int row, int col)
    {
        int count = 0;

        for (int i = 0; i < lights.length; i++) {
            if (lights[i][col]) {
                count ++;
            }
        }

        boolean light = lights[row][col];

        if (light) {
            return count % 2 == 0 ? false : light;
        } else {
            return count % 3 == 0 ? true : light;
        }
    }

    public void printBoard() {
        for (int r = 0; r < lights.length; r++) {
            for (int c = 0; c < lights[0].length; c++) {
                System.out.print((lights[r][c] ? "T" : "F") + " ");
            }
            System.out.println();
        }
    }
}

public class Main {
    public static void main(String[] args) {
        LightBoard board = new LightBoard(5, 5);
        System.out.println("Part A - Initial Board (T = true/on, F = false/off):");
        board.printBoard();
        
        System.out.println("Part B (row 1 col 1, row 2 col 2, ... row 5 col 5):");
        for (int i = 0; i < 5; i++) {
            System.out.println(board.evaluateLight(i, i));
        }
    }
}

Main.main(null)

Part A - Initial Board (T = true/on, F = false/off):
F T F F F 
F T F F T 
F T T F F 
F T T T F 
T T F F F 
Part B (row 1 col 1, row 2 col 2, ... row 5 col 5):
false
true
false
true
false

My process

Part A

• initialize the 2D array, then populate with booleans
• array created with preset row and column counts
• nested for loop to iterate through each row and column
• with Math.random(), get a random number from 0 to 1

Part B

• Identified the core requirement of the problem, to count the “on” lights in a column regardless of the specific light’s initial status.

• for loop iterated through the rows to calculate the total number of true values in the column.

• Stored the total in a count variable.

• Simplified the code by assigning lights[row][col] to a new boolean variable to avoid repetitive lookups.

• Evaluated the status of the light using an if/else structure.

• Implemented ternary operators within those conditions to check if the count was divisible by 2 or 3.

Struggles

Again, I struggled mostly with understanding what the problem was asking me to do. In order to get through the problem, I identified the core tasks and changed little bits of code at a time.