Domino Logic Puzzles

How it works

A domino logic puzzle starts with a grid of numbers and no dominoes on it. Somewhere in that grid a full set of dominoes is hidden, laid edge to edge with no gaps, and your job is to find where each one went. A full set holds every pair of numbers once, doubles included, so a set from 0 to 6 has 28 dominoes. Every number in the grid belongs to exactly one domino, and no pair may appear twice.

You solve it by working out where a pair can and cannot go. A double that fits in only one place is a sure thing. A number in a corner with only one free neighbour must pair with it. Each domino you lay removes its pair from the set, which rules out every other place that pair could have gone, and that often leaves another pair with only one spot. Bigger boards also need you to think about pockets of numbers that would be left stranded.

What makes a good one

• One answer, reachable by reasoning alone, with no guessing.
• Large, clear numbers that are easy to read on a phone.
• A list of the set that ticks pairs off as you lay them.
• A way to mark edges that cannot be a domino.
• Hints that name the next deduction, plus unlimited undo.

Strategies that help

Start with doubles. A double can only go where two equal numbers sit side by side, and there are often very few of those.

Check the corners and edges. A number with only one free neighbour has only one choice.

Use the set. Once a pair is laid, cross out every other place it could have gone.

Watch for odd pockets. A group of cells with an odd count can never be filled by dominoes, so any slab that would leave one behind is wrong.

Our take

Our domino logic puzzle is Pairstone. The grid is a stonemason’s yard of numbered cobbles, a set tray ticks each pair off, Mason’s Chalk names the next deduction, and the slabs topple in a chain when you finish. A Daily Yard of three boards is the same for everyone. For another kind of grid logic, see binary grid puzzles.