Solution.java

class Solution {
    public int[][] allCellsDistOrder(int rows, int cols, int rCenter, int cCenter) {
        Deque<int[]> q = new ArrayDeque<>();
        q.offer(new int[]{rCenter, cCenter});
        boolean[][] vis = new boolean[rows][cols];
        vis[rCenter][cCenter] = true;
        int[][] ans = new int[rows * cols][2];
        int idx = 0;
        int[] dirs = {-1, 0, 1, 0, -1};
        while (!q.isEmpty()) {
            for (int n = q.size(); n > 0; --n) {
                int[] p = q.poll();
                ans[idx++] = p;
                for (int k = 0; k < 4; ++k) {
                    int x = p[0] + dirs[k];
                    int y = p[1] + dirs[k + 1];
                    if (x >= 0 && x < rows && y >= 0 && y < cols && !vis[x][y]) {
                        q.offer(new int[]{x, y});
                        vis[x][y] = true;
                    }
                }
            }
        }
        return ans;
    }
}