Tents and Trees
It is hot in the holidays, and the campground is full of guests. Eveybody wants a spot in the shade of one of the nice trees that are scattered over the ground, but no-one likes to be too close to his neighbours.
Next to every tree there will have to be put a tent, either horizontally or vertically. Tents do not touch each other, not even diagonally. The numbers next to and below the diagram indicate how many tents there are in that particular row or column.
Mostly grids for this type of puzzle are quite large, but we will use a miniature version to serve as an example.
The first thing that strikes out in this diagram is the digit 0 next to the second row. With the right mouse button we can mark the corresponding squares with grass, so that we will never have to accidentally consider them as a candidate position for a tent. Now it becomes obvious that the tree in the upper right has her tent on her left side, there's no other valid position anymore. The second tent on the upper row is not allowed to touch the other, so only the box in the upper left remains.
In the second column we have to put 1 other tent and there's also just one square available, so we have little choice but to put it there. For the fourth and last tent is just one position that does not touch another tent, but does lie next to a tree that has no tent yet, so we can finish the puzzle. Note that it was also possible to tell this last fact by looking only at the numbers on the sides.
For clarity there is an option to draw lines from trees to tents, such that we can indicate to which tree which tent belongs. To activate this, click in the box where the particular tree was planted on the side where the tent is standing. For checking if the solution is correct however, this information is completely ignored.
This genre was invented by Léon Balmaekers and was first published in the Dutch puzzle magazine Breinbrekers in 1989, where it was named "Alle ballen verzamelen".
Puzzles in this genre