How the levels are made

The solver

Every level of Gridlock Escape comes from our own search, and its par is proven. This post explains how, with the numbers as they stood on 6 November 2026.

The solver is a breadth-first search. It starts from the board, tries every legal slide, then every legal slide from each of those positions, layer by layer, and never visits a position twice. The number of the first layer with a solved position in it is the par. A position is just the place of every vehicle along its lane, packed three bits per vehicle into one number, so a board of up to 8×8 squares and 17 vehicles fits in a single value.

The same solver gives the hints in the game: it solves the board as it stands and returns the first move. The guide to par and hints shows what that means for a player.

Finding boards

A new board starts as a random scatter of vehicles on the lot. The solver explores every position reachable from it, which we call the board’s cluster, and the generator keeps the position farthest from every solution. That position has the largest par the set of vehicles allows.

Random scatter finds plenty of easy and medium boards but stalls around 44 moves. To go further, the search takes the hardest boards it has and changes them a little: it moves, adds or swaps a vehicle, jumps to the hardest position of the new board, and keeps the change when the par does not drop and, now and then, when it does, the way simulated annealing does. These climbs push toward ever higher pars. A normal search runs for about twenty minutes, and a longer hunt looks only for the hardest boards.

The board database

Every distinct board any search finds goes into a database, in one canonical spelling, with one file per par. On 4 November it held 36,445 puzzles. A longer search on 5 November added 207,980 more, for 244,425 in all, from par 1 to par 51. They thin out quickly: 21,492 boards have par 4, and 125 have par 40 or more.

The database holds boards only, with no theme and no dressing. The vehicles, colours, hero and mission of a level are added by the game, and are fixed by the level’s number. A future set of levels could pick different boards from the same database and give them another look.

From the database to 200 levels

The level pack is picked, not designed. Level i of 200 gets the board whose par is nearest to a curve that rises from 3 moves to the hardest par available. With the curve we use that works out at about six levels per par value early on and three near the top: the pack has seven levels with par 3 and two each at 47, 48 and 49. Ties go to the board with fewer vehicles, then the smaller cluster, so the pick depends only on the database and takes seconds to repeat.

Boards reserved for the challenges are skipped, which is how they stay secret until their day, and no board of the pack is ever one of them.

Checking it

A separate check re-solves all 200 levels without using the generator’s answers. It confirms that every board is valid, that its par is the true minimum, that par never drops from one level to the next, that no two levels are the same puzzle at different points of its solution, and that every board is in our own database. Levels are never copied from a book, an app or a website, and a level that fails the check cannot ship.

The hardest board we have found

The hardest board in our database needs 51 moves, and the next hardest needs 50. Our own hunt found both, and the solver has proved both pars. The database holds what our searches have found and nothing else, so that is all we claim. The boards in the game come only from our searches.

A bigger lot is a different matter. The number of positions grows quickly with the size of the board, and we have no plan for one.