Walls and Gates

Source

• leetcode: 286

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, 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

Java

//BFS
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});
        }
    }
}