Dominosa Puzzles
A grid filled with numbers, no domino boundaries shown. A complete set of dominoes — 0-0 up to the highest double, every pair once — is hiding in the adjacent cells. Tap one cell, then tap a neighbour, and it locks in as that domino if the pair has not already been claimed.
Invented by O. S. Adler; also spelled domino solitaire.
Related Practice
What Is A Dominosa Puzzle?
Dominosa is a grid filled entirely with numbers, with no domino boundaries drawn anywhere. Hidden in it is a complete set of dominoes — every pair from 0-0 up to the highest double, each appearing exactly once on two cells that sit next to each other. The puzzle is finding which adjacent pair is which domino, using nothing but deduction: no domino can appear twice, and every cell belongs to exactly one.
It was invented in 1874 by O. S. Adler, which makes it one of the older puzzle formats on this site — most of the others here trace back to Japanese magazines a century later. The name is a play on "dominoes" and "solitaire," and it is sometimes called domino solitaire for exactly that reason.
Every Number Is Always Shown
Nothing about a dominosa grid is stripped for difficulty, the same call this site makes for shikaku and akari: every number is part of the puzzle from the start, because the numbers ARE what you reason from. What changes with difficulty here is the size of the domino set — a double-3 set has only 10 dominoes on a 4×5 grid; a double-6 set, the traditional full size, has 28 dominoes on a 7×8 grid and far more numbers repeating in far more places.
Why This Page Took Longer To Build Than It Looks
Unlike shikaku or akari, a random dominosa grid does not usually have only one answer. Because the same number can sit next to another copy of itself in several places by pure coincidence, most random layouts admit more than one valid way to pair up the dominoes — measured directly rather than assumed: only roughly one grid in twenty to one in thirty turned out to have a single, unambiguous solution, regardless of size. Of those, only a further slice can be solved by pure deduction with no guessing at all.
Both filters together are still cheap enough to check on the fly — each attempt costs a fraction of a millisecond — so every grid here is generated by trying random layouts and keeping only the rare one that is both uniquely solvable and provably guess-free, discarding the rest. Nothing is designed by hand and nothing is baked in advance; the filtering alone does the work.
What Actually Cracks A Dominosa
| Foothold | What it tells you | Why it works |
|---|---|---|
| A pair that only touches once | That is its domino, immediately | If two numbers sit adjacent in only one place on the whole grid, there is nowhere else that domino could be. |
| A cell with one neighbour left | Its domino is forced | Every cell belongs to exactly one domino, whatever the numbers involved, so a cell out of alternatives has no choice left. |
| A domino already placed | Every other matching pair nearby is impossible | No domino may appear twice, so any other adjacent pair showing the same two numbers is ruled out at once. |
| A double, like 4-4 | Often the rarest pair on the grid | Two identical numbers touching happens less often than an ordinary pair, which is exactly what makes it useful. |
Show me the next move plays this exact sequence and names which domino it is placing and why — never a guess dressed up as logic.
Dominosa Puzzles Frequently Asked Questions
What is a dominosa puzzle?
A grid of numbers with no domino boundaries shown, hiding a complete set of dominoes — every pair from 0-0 up to the highest double, each on exactly one adjacent cell pair. The puzzle is finding which pair is which domino.
Why are all the numbers given, unlike some of your other grids?
Because the numbers are what the whole puzzle is reasoning about, not a fact to be worked out separately. Shikaku and akari make the identical call for the identical reason — difficulty comes from the grid's size, not from information withheld.
What is the best way to solve a dominosa puzzle?
Look for two numbers that only sit next to each other in one place on the whole grid — that has to be their domino. Place it, cross out every other spot showing that same pair, and keep going: each placement usually forces the next one nearby.
Can the same domino appear twice?
No — a full set has exactly one of every pair, so once a domino is placed, no other adjacent cells anywhere in the grid may claim that same pair. The board will not let you place a duplicate.
Who invented dominosa?
O. S. Adler, in 1874. It is one of the oldest puzzle formats built on this site.
Is it free, and does it need an account?
Free, no account, no adverts, and nothing leaves your browser.