Work out where a full domino set once lay by reading a grid of numbers and placing each pair exactly once.
Dominosa Domino Logic starts after the dominoes are gone. Someone laid a complete set into a rectangle, wrote each half’s number on the board underneath and then cleared every tile away. You see only the grid of numbers. Your job is to work out where each domino was, so that every pair in the set turns up exactly once.
It is the Dominosa puzzle from a well-known open-source collection of small logic games.
How the board is built
The standard set runs from 0 to 6. A full set has one domino for each possible pair, doubles such as 4-4 included, which comes to 28 dominoes on an 8x7 grid. A set that goes up to some number N fills a board N+2 wide and N+1 tall.
Every domino covers two squares that sit next to each other, either side by side or one above the other. The puzzle is solved when the whole board is covered and no pair appears twice.
Placing and marking
Click the gap between two neighboring numbers to drop a domino across them, and click again to take it away. Laying a new domino on top of older ones removes the old ones. A right-click on a gap adds a small dash instead, which is your note that no domino belongs there.
If you place the same pair twice, both copies turn red, so you spot the clash quickly. Typing a number, or right-clicking it, lights up every square with that value. You can highlight up to two numbers at once.
Strategy notes
- Start with a lonely pair. Choose a pair like 2-5 and scan for every place it could go. If only one place remains, that domino is settled.
- Corner squares are clues. A square boxed in by the edge and by placed dominoes has only one free neighbor left to pair with.
- Rule out used pairs. Once a pair is down, mark lines across its other possible spots so you stop looking at them.
- Watch the doubles. Two equal numbers side by side may be the only home for that double, unless the grid offers another such spot.
Who it suits
This is a quiet, pen-and-paper style puzzle for people who like pure deduction with no luck involved. The Type menu lets you start with tiny sets and the Trivial setting, then work up through Basic, Hard and Extreme. Larger presets, with numbers up to 9, give long and absorbing sessions once the basic tricks feel natural.
Controls
| Action | Keyboard | Mouse | Touch |
|---|---|---|---|
| Place or remove a domino | Arrow keys to a spot between two numbers, then Enter | Left-click between two neighboring numbers | Tap between two neighboring numbers |
| Draw or erase a "no domino here" line | Space | Right-click between two numbers | Press and hold between two numbers |
| Highlight every copy of a number | Type the number | Right-click on the number | Press and hold on the number |
| Undo, redo, new puzzle | U / R / N | Undo move, Redo move and New game buttons | Undo move, Redo move and New game buttons |
Dominosa Domino Logic FAQ
Is Dominosa Domino Logic good on a phone or Chromebook?
Yes. On a touch screen you tap between two numbers to lay a domino and press and hold to draw a note line. On a Chromebook or computer you can use the mouse, or play entirely from the keyboard with the arrow keys, Enter and Space.
Does every puzzle have a solution?
Yes. The Trivial, Basic, Hard and Extreme settings always build a grid with one unique answer, so pure logic can reach it. The only exception is the Ambiguous option under Custom, which allows more than one correct layout.
What should I do if I get stuck?
Pick a single pair and look for every spot it could fit. Often only one spot is left. You can also highlight every copy of a number by typing it, and the Undo button steps back if a guess goes wrong.
How long does one puzzle take?
That depends on the set size and difficulty. A small preset with numbers up to 3 is a quick warmup, while the largest preset with numbers up to 9 covers a much bigger grid and can take a good while.
