Solution.java

class Solution {
    public int shortestDistance(int[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        Deque<int[]> q = new LinkedList<>();
        int total = 0;
        int[][] cnt = new int[m][n];
        int[][] dist = new int[m][n];
        int[] dirs = {-1, 0, 1, 0, -1};
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (grid[i][j] == 1) {
                    ++total;
                    q.offer(new int[] {i, j});
                    int d = 0;
                    boolean[][] vis = new boolean[m][n];
                    while (!q.isEmpty()) {
                        ++d;
                        for (int k = q.size(); k > 0; --k) {
                            int[] p = q.poll();
                            for (int l = 0; l < 4; ++l) {
                                int x = p[0] + dirs[l];
                                int y = p[1] + dirs[l + 1];
                                if (x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == 0
                                    && !vis[x][y]) {
                                    ++cnt[x][y];
                                    dist[x][y] += d;
                                    q.offer(new int[] {x, y});
                                    vis[x][y] = true;
                                }
                            }
                        }
                    }
                }
            }
        }
        int ans = Integer.MAX_VALUE;
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (grid[i][j] == 0 && cnt[i][j] == total) {
                    ans = Math.min(ans, dist[i][j]);
                }
            }
        }
        return ans == Integer.MAX_VALUE ? -1 : ans;
    }
}