Direction helper array

        int[][] dirs = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
        
        while (!queue.isEmpty()) {
            int[] cell = queue.poll();
            for (int[] d : dirs) {
                int r = cell[0] + d[0];
                int c = cell[1] + d[1];
                if (r >= 0 && r < m && c >= 0 && c < n) {
                    queue.add(new int[] {r, c});
                }
            }
        }