Mahjong solitaire — the 144-tile puzzle

Yes, with one important caveat. The board is built backwards: the program removes pairs from free places until the figure is empty, recording what it put where. That removal order is a ready-made solution, so a way out exists from the very start. But not every route works: one badly chosen pair of your own buries the tile you will need under someone else’s. Measured over twenty games of random play, eleven ran into a dead end, on average at move 33 out of 72 — which is exactly why the position is watched here.

It is the solver’s answer to “does a way to remove all remaining tiles still exist”. It is recomputed after every move in a separate thread, so the game never stutters. Sometimes you get “Cannot say” instead: the solver has a time budget, and lying that there is no way out where there is one would be worse than staying quiet.

An ordinary hint looks for any pair of free identical tiles. That move may be precisely the one that buries a tile you need. Here the hint comes out of a winning line: the solver first finds a way to clear the board to the end and shows its first move. Play the hint and you are guaranteed to stay in a position from which the board is still solvable.

Because there the remainder is laid out at random and the resulting position is never checked — a stalled board easily turns into a second stalled board. Here shuffling uses the same algorithm as dealing: the remainder is laid out backwards, so afterwards the board is solvable again. The cost is the move history — there is nothing left to undo, the board is a different one.

Then that tile is busy, and the game owes you an explanation. Tap it again: it shakes, highlights in yellow the tiles holding it, and a line appears next to it — covered from above or squeezed on both sides. Out of 144 tiles only a handful are free, so this is the normal state, not a breakage. To see the available tiles at a glance, turn on “Highlight free tiles” in settings.

They are two different games on the same set of tiles. Real mahjong is a Chinese four-player game with drawing, discarding and scoring for combinations, played around the circle of winds. The solitaire on those same tiles was invented for the computer in 1981: tiles are stacked into a figure and removed in pairs, and there is a single player. Only the set is shared — 108 suit tiles, winds, dragons, flowers and seasons.

The Turtle is the canon of the genre: 144 tiles, five layers, and the highest chance of a dead end. The Field is a single layer with nothing covering anything, so getting stuck is nearly impossible — a good place to start. Butterfly, Cat, Heart and Spider are full-size too but flat: two layers instead of five, so more tiles are free at any moment. The short ones — Warm-up at 40 tiles, Cross at 56 and Oval at 64 — take a few minutes and fit a phone screen without full-screen mode.

The set has 108 tiles in three suits, 16 winds, 12 dragons, plus four flowers and four seasons — one of each. If they required an exact match, eight tiles would simply have no partner and the board would never come out. So any flower pairs with any flower, and any season with any season.

That means your system has no font with Chinese characters — the winds, dragons and the “wan” symbol are drawn with them. The game checks for such a font on start and substitutes Latin letters when it is missing. You can also switch on “Letter codes” yourself: it adds a short code in the corner of every tile. The same panel has the “Contrast” theme — a white tile, a black outline and thick symbols.