LeetCode 286: Walls and Gates

class Solution {
    public void wallsAndGates(int[][] rooms) {
        if (rooms.length == 0 || rooms[0].length == 0) {
            return;
        }
        
        for (int i = 0; i < rooms.length; i++) {
            for (int j = 0; j < rooms[i].length; j++) {
                if (rooms[i][j] == 0) {
                    visit(rooms, i, j, 0);
                }
            }
        }
    }
    
    private void visit(int[][] rooms, int x, int y, int level) {
        if (rooms[x][y] == -1) {
            return;
        }
        
        if (level == 0 || rooms[x][y] > level) {
            if (level != 0) {
                rooms[x][y] = level;
            }
            if (x > 0) visit(rooms, x - 1, y, level + 1);
            if (x < rooms.length - 1) visit(rooms, x + 1, y, level + 1);
            if (y > 0) visit(rooms, x, y - 1, level + 1);
            if (y < rooms[0].length - 1) visit(rooms, x, y + 1, level + 1);
        }
    }
}