[LintCode] 663. Walls and Gates

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

-1 - A wall or an obstacle.
0 - A gate.
INF - Infinity means an empty room. We use the value 2^31 - 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, that room should remain filled with INF

Example

Example1

Input:
[[2147483647,-1,0,2147483647],[2147483647,2147483647,2147483647,-1],[2147483647,-1,2147483647,-1],[0,-1,2147483647,2147483647]]
Output:
[[3,-1,0,1],[2,2,1,-1],[1,-1,2,-1],[0,-1,3,4]]

Explanation:
the 2D grid is:
INF  -1  0  INF
INF INF INF  -1
INF  -1 INF  -1
  0  -1 INF INF
the answer is:
  3  -1   0   1
  2   2   1  -1
  1  -1   2  -1
  0  -1   3   4

Example2

Input:
[[0,-1],[2147483647,2147483647]]
Output:
[[0,-1],[1,2]]

public class Solution {
    /**
     * @param rooms: m x n 2D grid
     * @return: nothing
     */
    public void wallsAndGates(int[][] rooms) {
        // write your code here
        Queue<Cell> queue = new LinkedList<>();
        int row = rooms.length;
        int col = rooms[0].length;
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if (rooms[i][j] == 0) {
                    // x correspond to i => row, y correspond to j => col
                    // start from the smallest point
                    queue.offer(new Cell(i, j, rooms[i][j]));
                }
            }
        }
        
        int[][] directions = new int[][]{{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
        while (!queue.isEmpty()) {
            Cell cur = queue.poll();
            for (int[] dir: directions) {
                int newX = cur.x + dir[0];
                int newY = cur.y + dir[1];
                if (newX >= 0 && newX < row && newY >= 0 && newY < col && rooms[newX][newY] == Integer.MAX_VALUE) {
                    rooms[newX][newY] = cur.val + 1;
                    queue.offer(new Cell(newX, newY, rooms[newX][newY]));
                }
            }
        }
    }
}

class Cell {
    int x;
    int y; 
    int val;
    public Cell(int x, int y, int val) {
        this.x = x;
        this.y = y;
        this.val = val;
    }
}