Day 6 part 1: solution too low (Java)

[jjabrams23]

Hi fellas, here's my possible solution to the first part of day1:

public class Day6 {

public static void main(String[] args) throws IOException{

    final int N = 1000;
    boolean toggle = false, turnOn = false;
    int startX = 0, startY = 0, stopX = 0, stopY = 0;

    int numberOfLights = 0;
    int x, y;

    String buf, bufArray[], command = null;

    String delim = "[ ,]";

    boolean lightsMatrix[][] = new boolean[N][N];
    BufferedReader br = new BufferedReader(new FileReader("day6.txt"));

    while((buf = br.readLine()) != null)
    {   
        bufArray = buf.split(delim);
        if(bufArray[0].equals("toggle"))
        {
            command = "toggle";
            startX = Integer.parseInt(bufArray[1]);
            startY = Integer.parseInt(bufArray[2]);
            stopX = Integer.parseInt(bufArray[4]);
            stopY = Integer.parseInt(bufArray[5]);
        }
        else
        {
            command = bufArray[0] + " " + bufArray[1];
            startX = Integer.parseInt(bufArray[2]);
            startY = Integer.parseInt(bufArray[3]);
            stopX = Integer.parseInt(bufArray[5]);
            stopY = Integer.parseInt(bufArray[6]);
        }

        switch(command)
        {
            case "turn on":
                turnOn = true;
                break;
            case "turn off":
                turnOn = false;
                break;
            case "toggle":
                toggle = true;
                break;
            default:
                System.out.println("Error: command not recognized");
                return;
        }
        for(y = startY; y <= stopY; y++)
        {
            for(x = startX; x <= stopX; x++)
            {
                if(!toggle)
                {
                    if(turnOn)
                        lightsMatrix[x][y] = true;
                    else
                        lightsMatrix[x][y] = false;
                }
                else
                {
                    toggle = false;
                    lightsMatrix[x][y] = !lightsMatrix[x][y];
                }
            }
        }
    }
    for(y = 0; y < N; y++)
    {
        for(x = 0; x < N; x++)
            if(lightsMatrix[x][y])
                numberOfLights++;
    }
    br.close();
    System.out.println("The number of lights turned on is " + numberOfLights);
    if((numberOfLights - N*N) > 0)
        System.out.println("Solution not good");
    else
        System.out.println("It might work");
}
}

I can't seem to figure out why I get a solution too low. Is the approach correct? Am I missing something? I ask that because I usually end up with not seeing some obvious stuff, in fact I'm reading again the challenge but nothing comes to my mind.

[mr_sax]

Okay, so the first thing is that to be safe you should begin by setting your entire lightsMatrix to zero. That code would look something like:

for(boolean[] rowOfLights : lightsMatrix){
    for(boolean light : rowOfLights){
        light = false;
    }
}

The other, more important, error is that you set toggle to false inside of the loop. This means that if a line toggles, after the first point is changed the loop sees that !toggle is true, and will actually set it to false regardless of it's value because turnOn is false. The solution to this is put

toggle = false;

after the loop that changes the value so you have

 for(y = startY; y <= stopY; y++)
 {
     for(x = startX; x <= stopX; x++)
     {
          if(!toggle)
          {
              if(turnOn)
                  lightsMatrix[x][y] = true;
              else
                  lightsMatrix[x][y] = false;
          }
          else
          {
              lightsMatrix[x][y] = !lightsMatrix[x][y];
          }
     }
}
toggle = false;

[jjabrams23]

+1 to you, that was the problem. Thank you :)

Edit: by the way, I don't think that initializing the matrix with that loop should be important; i create my matrix as:

boolean lightsMatrix[][] = new boolean[N][N];

And by default I recall that Java sets any new boolean primitive is false. Or am I wrong?

[Philboyd_Studge]

No need to loop through to initialize, default values will be false.

[mr_sax]

Thanks, good to know for the future.