Puzzle Difficulty Estimation

One of the key properties of a puzzle is the difficulty. When presenting a player with a sequence of puzzles, it is vital that they are at the right difficulty level – if the puzzles are too easy, players will become bored; if they are too hard, players will become frustrated. Ideally, puzzles in a sequence will increase slightly in difficulty, so as to keep the player engaged.

Existing puzzle games show exactly this pattern. However, there is a clear drawback: puzzles are hand-designed. While hand-designed puzzles will always have their place in the gaming world, it is simply not feasible to present all players of a mobile puzzle game with personalised hand-made content.

We developed a method to estimate the difficulty of puzzle game instances based on a small set of easy-to-compute game features. The method requires a small number of puzzles to be judged by play-testers, but can then automatically assign difficulty scores to any number of instances of the same puzzle game. It has been tested on three very different puzzle games and can estimate difficulty roughly with a one-star error, if difficulty is measured on a scale of 1 to 10 stars.