PostOffices.java

import java.util.Arrays;
import java.util.LinkedList;
import java.util.Queue;

class Solution {
	class Coor {
		int x, y, d;

		Coor(int x, int y, int d) {
			this.x = x;
			this.y = y;
			this.d = d;
		}
	}

	private int[][] dirs = new int[][] { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } };

	public int[][] postOffices(int row, int col, int[][] offices) {
		int[][] result = new int[row][col];
		for (int[] r : result) {
			Arrays.fill(r, -1);
		}

		Queue<Coor> queue = new LinkedList<>();

		for (int[] coor : offices) {
			result[coor[0]][coor[1]] = 0;
			Coor c = new Coor(coor[0], coor[1], 0);
			queue.add(c);
		}

		while (!queue.isEmpty()) {
			Coor front = queue.remove();

			for (int[] dir : dirs) {
				int x = front.x + dir[0];
				int y = front.y + dir[1];

				if (x < 0 || x >= row || y < 0 || y >= col || result[x][y] != -1)
					continue;
				result[x][y] = front.d + 1;
				queue.add(new Coor(x, y, front.d + 1));
			}
		}

		return result;
	}
}