ref: zergling-rush
Your task is to visualize what the base will look like after the zerglings arrive.
Note 1: zerglings enter from all sides (top, left, right, bottom).
Note 2: if no building can be reached or if there are no buildings at all, the zerglings will not stay (no zerglings should be included in the output).
For example, a base like:
...#####
...#...#
..B..B.#
...#...#
...#####
will become
...#####
.zz#...#
.zB..B.#
.zz#...#
...#####
Zerglings surround the building to the left, but cannot access the building to the right because their path is blocked.