Campsite

Campsite, also known as Tents or Tents And Trees, is a placement puzzle which first came to our attention in the Dutch magazine 'Brein Brekers', and appeals due to the interesting logic deriving from its small number of simple rules.

In a rectangular grid, a number of trees are placed; each tree has one tent 'tied' to it in a neighbouring square, and the number of tents to be placed in each row and column is also given. It should be noted, by the way, that a tent cannot be placed in the same square as a tree. The major rule which makes the puzzle solvable, however, is that no two tents can be in touching squares, even if they touch only at a corner – and it is this constraint which suggests some solving strategies to apply.

As with many puzzles of similar form, the methodical approach here is to use a process of elimination. It may be possible to conclude that a pair of neighbouring squares must contain one tent, even though it isn't yet known which one; however, up to four adjoining squares can be eliminated as a result, as they touch both. By similar logic, if a tent must go into a 1x3 region, then up to two adjoining squares can be eliminated.

Another line of attack, which helps somewhat in the sample puzzle here, is to tackle two adjacent rows as a whole, keeping in mind that a 2x2 box can contain at most one tent.

Campsite puzzles were a regular feature in 'Tough Puzzles' from 2004 to 2007.