BFS2D.java

public List<Cell> runBFS2D(Vec2D startCoords) {
        List<Cell> positiveMatches = new ArrayList();
        final String queryProperty = getProperty(startCoords);

        Cell firstCell = new Cell(startCoords);
        positiveMatches.add(firstCell);

        for (int i = 0; i < positiveMatches.size(); i++) {

            Cell thisCell = positiveMatches.get(i);

            for (int direction = 0; direction < 8; direction++) { 
                if (!thisCell.hasNeighbour(direction)) {
                    Cell newCell = new Cell(newCoords);
                    thisCell.setNeighbour(newCell, direction);
                    newCell.setNeighbour(thisCell, (direction + 4) % 8);
                    if (direction > 0) {
                        Cell oldCell = thisCell.getNeighbour(direction - 1);
                        int oldNewDir = (((direction + 1) / 2) * 2 + 1) % 8; //since we are dealing with integers, the "/ 2" gets rounded down.
                        oldCell.setNeighbour(newCell, oldNewDir);
                        newCell.setNeighbour(oldCell, (oldNewDir + 4) % 8);

                        if (direction == 7) {
                            Cell veryOldCell = thisCell.getNeighbour(0);
                            veryOldCell.setNeighbour(newCell, 5);
                            newCell.setNeighbour(veryOldCell, 1);
                        }
                    }
                  
                    int xDiff;
                    int yDiff;
                    if (direction < 3) {
                        xDiff = -1;
                    } else if (direction % 4 == 3) {
                        xDiff = 0;
                    } else {
                        xDiff = 1;
                    }
                    int yCounter = (direction + 2) % 8;
                    if (yCounter < 3) {
                        yDiff = -1;
                    } else if (yCounter % 4 == 3) {
                        yDiff = 0;
                    } else {
                        yDiff = 1;
                    }
                  
                    Vec2D newCoords = thisCell.getCoords().transform(xDiff, yDiff);
                    if (queryProperty.equals(getProperty(newCoords))) {
                        positiveMatches.add(newCell);
                    }
                }
            }
        }
        return positiveMatches;
    }