Sliding Tile Puzzle Tips: 3 Stars Cost 2.5x the Moves

The first sliding tile puzzle tip is to plan the whole star route before you close the path: in Groovetile the shortest way to finish levels 1 to 5 took 14 moves and earned only 6 of the 15 stars, while the shortest three-star solutions took 36 moves. The level ends the moment the grooves connect, so a quick finish can lock you out of the stars.

How Groovetile works

Groovetile is a sliding tile puzzle on a four by four board. A metal ball sits on a blue start tile, a red goal tile sits somewhere else, and the squares between them hold wooden tiles with grooves cut into them, plus a couple of empty squares. Dragging a plain wooden tile into an empty neighbour moves it one square; the start, the goal and grey tiles with screws stay where they are. When the grooves form one unbroken path from start to goal, the ball rolls along it and the level is over. Some tiles carry a star, and the level awards one star for each star tile on the ball’s path, up to three.

What we measured

We played levels 1 to 5 of the first pack. For each level we copied the board from the screen into a small search program that tried every possible sequence of slides, with the same rule as the game: once the path is complete, the level ends. It found two answers per level: the fewest moves to finish at all, and the fewest moves to finish with all three stars. We then played every one of those solutions in the game by dragging the tiles and checked the stars on the Level Completed card. Every three-star solution earned three stars in the game.

Moves count single-square slides. The boards were copied by hand from screenshots and every solution was replayed in the game. The search shows the fewest moves possible; a person will usually need a few more.

The quick finish is a trap

On level 2 a single slide completes the path, but the path passes only one of the three star tiles. On levels 3 and 4 the shortest path skips every star: five and four moves for zero stars. Because the ball starts rolling the instant the grooves connect, you cannot fix it afterwards. If you want the stars, keep the path open until the star tiles are in place.

Three stars cost about 2.5 times the moves

Over the five levels the three-star routes needed 36 moves against 14 for the quickest finishes. Level 3 was the longest at 14 moves, and the search had to look through 172,449 board positions to be sure nothing shorter existed. Only level 1 gave three stars for the shortest answer, a single slide.

Make room first

The three-star solutions often begin the same way: a tile slides into an empty square away from the path to make room, and only then do the star tiles move into line. On level 2, for example, the first of the seven moves parks a corner tile in the empty left column.

4 tips that follow from the numbers

• Trace the star route first. Find a path from start to goal that crosses every star tile before you slide anything.
• Do not close the path early. The level ends at once, stars or not.
• Budget extra moves. Three stars took 2.5 times the moves of the quickest finish.
• Use empty corners as parking. Moving spare tiles out of the way comes before building the path.

Where to try it

Try it yourself in Groovetile. For another path puzzle, Valvewise has you turn pipes against a pressure gauge, and Pathloom is a maze game.