You can solve the mission Boundary Blocks first, it can be a small useful part for this one.

This mission is an adaptation of the "Range" game (from Simon Tatham's Portable Puzzle Collection ). If you are lost or just want to play, the game is available here .

You're on a rectangular grid. Each numbered box corresponds to the number of empty cells in all four directions from it (but not diagonally), including itself. In order to satisfy these requirements, you have to arrange black boxes in empty cells to limit visibility.

Two additional rules:

• Two black boxes can't be neighbors horizontally or vertically.
• Black boxes can't separate white cells into several parts.

Empty boxes are represented by zeros.

Then, you have to return the coordinates of black boxes.

Black boxes at (1, 2), (0, 0), (2, 3), (3, 4) and (2, 0).
[[0, 0, 4, 0, 6],
 [0, 6, 0, 0, 0],
 [0, 0, 0, 0, 0],
 [0, 0, 0, 5, 0],
 [6, 0, 7, 0, 0]]

Input: A list of lists of integers.

Output: An iterable of tuples/lists of two integers.

list(visibilities([[0, 0, 4, 0, 6],
                   [0, 6, 0, 0, 0],
                   [0, 0, 0, 0, 0],
                   [0, 0, 0, 5, 0],
                   [6, 0, 7, 0, 0]])) == [(1, 2), (0, 0), (2, 3), (3, 4), (2, 0)]

Preconditions:

• Given puzzles are solvable.
• 5 ≤ len(grid) ≤ 50 and 5 ≤ len(grid[0]) ≤ 50.
• all(len(row) == len(grid[0]) for row in grid).