286. Walls and Gates

You are given a m x n 2D grid initialized with these three possible values.

1. -1 - A wall or an obstacle.
2. 0 - A gate.
3. INF - Infinity means an empty room. We use the value 231 - 1 = 2147483647 to represent INF as you may assume that the distance to a gate is less than 2147483647.

Fill each empty room with the distance to its nearest gate. If it is impossible to reach a gate, it should be filled with INF.

For example, given the 2D grid:

INF  -1  0  INF
INF INF INF  -1
INF  -1 INF  -1
  0  -1 INF INF

After running your function, the 2D grid should be: 

  3  -1   0   1
  2   2   1  -1
  1  -1   2  -1
  0  -1   3   4   

将 gate 做dfs 或者存入queue

    public void wallsAndGates(int[][] rooms) {
        for(int i = 0; i< rooms.length; i++){
            for(int j = 0; j < rooms[0].length; j ++){
                if(rooms[i][j] == 0)
                    dfs(rooms, i, j, 0);
            }
        }
    }
    public void dfs(int[][] rooms, int i , int j, int deep){
        rooms[i][j] = deep;
        if(i < rooms.length - 1 && rooms[i+1][j] > deep)
            dfs(rooms, i + 1, j, deep +1);
        
        if(j < rooms[0].length - 1 && rooms[i][j + 1] > deep)
           dfs(rooms, i, j + 1, deep +1);

       if(j > 0 && rooms[i][j - 1] > deep)
            dfs(rooms, i, j - 1, deep +1);
        
       if(i > 0 && rooms[i-1][j] > deep)
            dfs(rooms, i - 1, j, deep +1);
    }

BFS

class Node{
    int x;
    int y;
    public Node(int x, int y){
        this.x = x;
        this.y = y;
    }
}
private  int inf = Integer.MAX_VALUE;
    public  void wallsAndGates(int[][] nums){
        Queue<Node> queue = new LinkedList<>();
        for(int i = 0 ; i < nums.length; i++){
            for(int j = 0; j < nums[0].length; j ++){
                if(nums[i][j] == 0){
                    Node x = new Node(i,j);
                    queue.add(x);
                }
            }
        }
        bfs(queue, nums);
    }
    public  void bfs(Queue<Node> queue, int[][] nums){
        while(!queue.isEmpty()){
            Node root = queue.poll();
            int x = root.x;
            int y = root.y;
            if(x < nums.length - 1 && nums[x+1][y] == inf){
                nums[x+1][y] = nums[x][y] + 1;
                queue.add(new Node(x+1,y));
            }
            if(x > 0 && nums[x-1][y] == inf){
                nums[x-1][y] = nums[x][y] + 1;
                queue.add(new Node(x-1,y));
            }
            if(y < nums[0].length - 1 && nums[x][y+1] == inf){
                nums[x][y+1] = nums[x][y] + 1;
                queue.add(new Node(x,y+1));
            }
            if(y > 0 && nums[x][y-1] == inf){
                nums[x][y-1] = nums[x][y] + 1;
                queue.add(new Node(x,y-1));
            }
        }
    }

}