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

public class Solution {
    public void wallsAndGates(int[][] rooms) {
        if (rooms.length == 0 || rooms[0].length == 0) return;
        Queue<int[]> queue = new LinkedList<>();
        for (int i = 0; i < rooms.length; i++) {
            for (int j = 0; j < rooms[0].length; j++) {
                if (rooms[i][j] == 0) queue.add(new int[]{i, j});
            }
        }
        while (!queue.isEmpty()) {
            int[] top = queue.remove();
            int row = top[0], col = top[1];
            if (row > 0 && rooms[row - 1][col] == Integer.MAX_VALUE) {
                rooms[row - 1][col] = rooms[row][col] + 1;
                queue.add(new int[]{row - 1, col});
            }
            if (row < rooms.length - 1 && rooms[row + 1][col] == Integer.MAX_VALUE) {
                rooms[row + 1][col] = rooms[row][col] + 1;
                queue.add(new int[]{row + 1, col});
            }
            if (col > 0 && rooms[row][col - 1] == Integer.MAX_VALUE) {
                rooms[row][col - 1] = rooms[row][col] + 1;
                queue.add(new int[]{row, col - 1});
            }
            if (col < rooms[0].length - 1 && rooms[row][col + 1] == Integer.MAX_VALUE) {
                rooms[row][col + 1] = rooms[row][col] + 1;
                queue.add(new int[]{row, col + 1});
            }
        }
    }

}

public class Solution {
    public void wallsAndGates(int[][] rooms) {
        if(rooms == null || rooms.length == 0){
            return;
        }
        for(int i=0; i<rooms.length; i++){
            for(int j=0; j<rooms[0].length; j++){
                if(rooms[i][j] == 0){
                    dfs(i, j, rooms, 1);
                }
            }
        }
        return;
    }
    
    public void dfs(int i, int j, int[][] rooms, int value){
        if(i<0 || i>=rooms.length || j<0 || j>=rooms[0].length){
            return;
        }
        if(valid(i, j+1, rooms) && rooms[i][j+1] > value){
            rooms[i][j+1] = value;
            dfs(i, j+1, rooms, value+1);
        }
        if(valid(i, j-1, rooms) && rooms[i][j-1] > value){
            rooms[i][j-1] = value;
            dfs(i, j-1, rooms, value+1);
        }
        if(valid(i+1, j, rooms) && rooms[i+1][j] > value){
            rooms[i+1][j] = value;
            dfs(i+1, j, rooms, value+1);
        }
        if(valid(i-1, j, rooms) && rooms[i-1][j] > value){
            rooms[i-1][j] = value;
            dfs(i-1, j, rooms, value+1);
        }
    }
    
    public boolean valid(int i, int j, int[][] rooms){
        if(i<0 || i>=rooms.length || j<0 || j>=rooms[0].length){
            return false;
        }
        return true;
    }
}