build post office II

def shortestDistance(self, grid):
        # write your code here
        if len(grid) == 0 or len(grid[0]) == 0:
            return -1
            
        max_row, max_col, direction_array = len(grid), len(grid[0]), [[0,1],[1,0],[-1,0],[0,-1]]
        targets, result, distance, reach = [], math.inf, [[0 for j in range(max_col)] for i in range(max_row)], [[0 for j in range(max_col)] for i in range(max_row)]
        
        for i in range(max_row):
            for j in range(max_col):
                if grid[i][j] == 1:
                    targets.append(i*max_col+j)
        
        for val in targets:
            bfs_queue, set_visit, dist = [val], set(), 0
            set_visit.add(val)
            while len(bfs_queue) > 0:
                size = len(bfs_queue)
                dist += 1
                for i in range(size):
                    node = bfs_queue.pop(0)
                    row, col = int(node / max_col), node % max_col
                    for add_row, add_col in direction_array:
                        new_row, new_col = row + add_row, col + add_col
                        new_val = new_row * max_col + new_col
                        if new_row >= 0 and new_row < max_row and new_col >= 0 and new_col < max_col and grid[new_row][new_col] == 0 and new_val not in set_visit:
                            reach[new_row][new_col] += 1
                            distance[new_row][new_col] += dist
                            bfs_queue.append(new_val)
                            set_visit.add(new_val)
        
        for row in range(max_row):
            for col in range(max_col):
                if grid[row][col] == 0 and reach[row][col] == len(targets):
                    result = min(result, distance[row][col])
            
        if result != math.inf:
            return result
        return -1