A light and shadow puzzle.
Here is the initial board state:
We can first separate regions of the same color, then extend regions as necessary:
Note that the rightmost black 5 can extend downward at most one cell and thus must extend at least twice to the right, which in turn forces the white region above:
Now, here comes the most crucial step. After making the red and blue expansions shown in the image below, we must decide how to route the circled white cell. Note that if we route it up (green path), it suffocates the green 5 region. Therefore, it must be routed to the right, which gives the yellow 5 region barely enough space.
After several expansions, we arrive here:
Now, note that the leftmost black ? must come out to the right, otherwise the solution would not be unique:
We now must decide how to route the circled black cell. This time, it can’t go up along the red path, so it must come down along the blue path:
From here, completing the puzzle is easy!
