[LeetCode] 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

Thought process:
Iterate through the grid. Add gates' coordinates to queue. BFS from gates and expand through all rooms.

Solution:

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public class Solution {
    private final int[][] DIRECTIONS = { { -1, 0 }, { 0, -1 }, { 1, 0 }, { 0, 1 } };
    
    public void wallsAndGates(int[][] rooms) {
        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.offer(new int[]{ i, j });
                }
            }
        }
        
        while (!queue.isEmpty()) {
            int[] room = queue.poll();
            int distance = rooms[room[0]][room[1]];
            
            for (int i = 0; i < 4; i++) {
                int row = room[0] + DIRECTIONS[i][0];
                int column = room[1] + DIRECTIONS[i][1];
                
                if (row >= 0 && row < rooms.length && column >= 0 && column < rooms[0].length) {
                    if (rooms[row][column] == Integer.MAX_VALUE) {
                        rooms[row][column] = distance + 1;
                        queue.offer(new int[]{ row, column });
                    }
                }
            }
        }
    }
}

Time complexity:
Each vertex's number of edges is constant. The overall time complexity is O(V).
Location: San Jose, CA, USA

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