2021 June bugfix:

- The generator assumed that at least 1 apple will be spawn. Now it is fixed and instances
can be generated where no apples are spawn (you only need to pick the ones that were
already there).

- Reduced the maximum number of apples by 1 when the grid has an odd number of cells, as
  they may be hamiltonian paths. This ensures that all instances using an empty grid are
  solvable (if other types of grids are used solvability needs to be ensured by other
  means).


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Instance Generator for Snake

Alvaro Torralba <torralba@cs.uni-saarland.de>
Florian Pommerening <florian.pommerening@unibas.ch>


In the game Snake, a snake moves around a grid. There is a number of apples in some grid
cells and when the snake moves into one of these locations, it eats the apple, extends its
length by one, and a new apple may spawn. In this version uncertainty has been removed by
deciding the location where apples will spawn in advance. Except for the end of the game,
there will be more than one apple on the board at the same time.

Interesting properties: dead-end states
