As Far from Land as Possible

Given an N x N grid containing only values 0 and 1, where 0 represents water and 1 represents land, find a water cell such that its distance to the nearest land cell is maximized and return the distance.

The distance used in this problem is the Manhattan distance: the distance between two cells (x0, y0) and (x1, y1) is |x0 - x1| + |y0 - y1|.

If no land or water exists in the grid, return -1.

Example 1:

Input: [[1,0,1],[0,0,0],[1,0,1]]
Output: 2
Explanation: 
The cell (1, 1) is as far as possible from all the land with distance 2.

Example 2:

Input: [[1,0,0],[0,0,0],[0,0,0]]
Output: 4
Explanation: 
The cell (2, 2) is as far as possible from all the land with distance 4.

Note:

1. 1 <= grid.length == grid[0].length <= 100

2. grid[i][j] is 0 or 1

class Solution {
    int[][] directions = new int[][] { { -1, 0 }, { 1, 0 }, { 0, -1 }, { 0, 1 } };

    public int maxDistance(int[][] grid) {
        if (grid == null || grid.length == 0 || grid[0].length == 0)
            return -1;
        boolean[][] visited = new boolean[grid.length][grid[0].length];
        Queue<int[]> queue = new ArrayDeque<>();
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j] == 1) {
                    queue.add(new int[] { i, j });
                    visited[i][j] = true;
                }
            }
        }
        int level = -1;
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                int[] start = queue.poll();
                int x = start[0];
                int y = start[1];
                for (int[] dir : directions) {
                    int newX = x + dir[0];
                    int newY = y + dir[1];
                    if (newX >= 0 && newX < grid.length && newY >= 0 && newY < grid[0].length && !visited[newX][newY]) {
                        visited[newX][newY] = true;
                        queue.add(new int[] { newX, newY });
                    }
                }
            }
            level++;
        }
        // If no land or water exists in the grid, return -1
        return level <= 0 ? -1 : level;
    }
}