2019 FRQ 4 Post

The LightBoard class models a two-dimensional display of lights, where each light is either on or off, as represented by a Boolean value. You will implement a constructor to initialize the display and a method to evaluate a light.

public class LightBoard {
    // 2D array storing all of the boolean light values (true indicates a light is on, while false indicates a light is off)
    private boolean[][] lights;
    
    // Constructor that initializes all of the random boolean values in the 2D array. Each light has a 40% chance of being on
    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++) {
                int randNumber = (int) Math.floor(Math.random() * 10) + 1;
                // Use of ternary operator to concise code
                boolean boolValue = (randNumber <= 4) ? true : false;
                lights[i][j] = boolValue;
            }
        }
    }

    // boolean method that returns false if the selected light is on and if the number of lights that are on in its column is even
    // returns true if the selected light is off and if the number of lights that are on in its column is divisible by 3 (Note that 0 is divisible by any number except itself)
    // returns lightStatus if the previous 2 conditions are not met
    public boolean evaluateLight(int row, int col) {
        boolean lightStatus = lights[row][col];
        int lightOnCount = 0;
        for (int i = 0; i < lights[col].length; i++) {
            if (lights[i][col] == true) {
                lightOnCount++;
            }
        }
        if (lightStatus == true && lightOnCount % 2 == 0) {
            return false;
        } else if (lightStatus == false && lightOnCount % 3 == 0) {
            return true;
        }
        return lightStatus;
    }

    // main tester method for running the code in the LightBoard class
    public static void main(String[] args) {
        LightBoard myObj = new LightBoard(4, 4);
        for (int x = 0; x < myObj.lights.length; x++) {
            for (int y = 0; y < myObj.lights[x].length; y++) {
                System.out.print(myObj.lights[x][y] + " ");
            }
            System.out.println("");
        }

        System.out.println("");
        System.out.println("evaluateLight method output: " + myObj.evaluateLight(1, 1));
    }
}

LightBoard.main(null);

false false false false 
true true false false 
false false true true 
false false true false 

evaluateLight method output: true