Question

I have this 2D array (say double[10][10]) which contain some 1.0 and 10.0, rest are all in 0.0s. I am trying to loop through this array to find the 1.0 (start point), from there ‘move’ it randomly (using random.nextInt(4)) up, down, left or right till it gets to 10.0. I created a emptyArray to keep track of how many time it had moved pass each point (or at least I think I did). Nothing came up when I compile but I do not get any result when I try to display it into a frame. Any idea where I had gone wrong or missing?

{0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,1.0,1.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,10.0,10.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,10.0,10.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}
{0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0}

Sample of 2D array.

    double[][] getPath(double[][] dataIn) {
    double[][] emptyArray = new double[dataIn.length][dataIn[0].length];
    double[][] drunkLoc = new double[dataIn.length][dataIn[0].length];
    for (int i = 0; i < dataIn.length; i++) {
        for (int j = 0; j < dataIn[i].length; j++) {
            if (dataIn[i][j] == 1.0) {

                double drunkHome = 10.0;
                drunkLoc[i][j] = dataIn[i][j];
                do {
                    int dir = getDirection();
                    switch(dir) {
                        case 0: 
                            if ((i > 0) && (j > 0)) {
                                drunkLoc[i][j] = drunkLoc[i-1][j];
                                double value = emptyArray[i][j];
                                emptyArray[i][j] = value + 1;
                                emptyArray[i][j] = (255<<24)  | (255<<16) | (255<<8) | 255;
                            } else {
                                break;
                            }
                            break;
                        case 1: 
                            if ((i > 0) && (j > 0)) {
                                drunkLoc[i][j] = drunkLoc[i][j-1];
                                double value = emptyArray[i][j];
                                emptyArray[i][j] = value + 1;
                                emptyArray[i][j] = (255<<24)  | (255<<16) | (255<<8) | 255;
                            } else {
                                break;
                            }
                            break;
                        case 2: 
                            if ((i > 0) && (j > 0)) {
                                drunkLoc[i][j] = drunkLoc[i+1][j];
                                double value = emptyArray[i][j];
                                emptyArray[i][j] = value + 1;
                                emptyArray[i][j] = (255<<24)  | (255<<16) | (255<<8) | 255;
                            } else {
                                break;
                            }
                            break;
                        case 3: 
                            if ((i > 0) && (j > 0)) {
                                drunkLoc[i][j] = drunkLoc[i][j+1];
                                double value = emptyArray[i][j];
                                emptyArray[i][j] = value + 1;
                                emptyArray[i][j] = (255<<24)  | (255<<16) | (255<<8) | 255;
                            } else {
                                break;
                            }
                            break;
                        default:
                    }
                } while (drunkLoc[i][j] != drunkHome);
            }
        }
    }
    return emptyArray;
}

Do let me know if you need any more clarification. Only my second post so still learning on my questioning technique. Thanks in advance.

Answer 1

OK, for you to study, here’s some sample code that will give you the answer you’re looking for (the number of moves to get from (xpos,ypos) to (destX,destY) on a “board” that is penDimension x penDimension in size:

        int penDimension = 10;
        int destX = 2;
        int destY = 2;
        int xpos = 5;
        int ypos = 5;

        // Add this to keep track of no moves through each square
        int[][] moveCounts = new int[penDimension][penDimension];

        Random r = new SecureRandom();
        long noMoves = 0;
        while (xpos != destX || ypos != destY) {
            switch (r.nextInt(4)) {
            case 0 : xpos++; break;
            case 1 : xpos--; break;
            case 2 : ypos++; break;
            case 3 : ypos--; break;
            }
            if (xpos < 0) xpos = 0;
            if (ypos < 0) ypos = 0;
            if (xpos > penDimension) xpos = penDimension;
            if (ypos > penDimension) ypos = penDimension;
            noMoves++;

            // Add this to keep track of no moves through each square
            moveCounts[ypos][xpos]++;

        }
        System.out.println("Number of moves: " + noMoves);

Instead of doing ++ or — and then checking the bounds afterwards, you could also write (and in real life probably would write) e.g.:

xpos = Math.max(0, xpos - 1);

I just wrote it as I did above because I thought it would be easier to understand.

Instead of writing “new SecureRandom()”, you could also write “new Random()”, which is probably what you’ve learnt. But SecureRandom is a much higher quality (but slower) random number generator. In general when writing ‘simulations’ where you are repeatedly generating a large number of random numbers, it’s better to avoid the standard Random class and use a higher quality generator.