Think of a box of dominoes tipped out face up, with all the lines between them gone. Your job is to find where each domino lies.
The rules
- The board is full of numbers. The numbers stay where they are.
- Join every number to 1 number next to it: above, below, left or right. Each joined pair is a domino.
- Every box belongs to exactly 1 domino.
- The basket shows the pairs you must use. Use each pair exactly once.
- 0-1 and 1-0 are the same pair. The order of the numbers does not matter.
- Doubles count too. A pair like 2-2 is in the set once.
These are the classic rules. The basket always holds a full set: every pair from 0-0 up to the highest number on the board.
A worked example
This board has 3 rows and 4 columns. It uses the numbers 0, 1 and 2.
| Column 1 | Column 2 | Column 3 | Column 4 | |
|---|---|---|---|---|
| Row 1 | 2 | 2 | 2 | 0 |
| Row 2 | 1 | 1 | 0 | 0 |
| Row 3 | 1 | 1 | 0 | 2 |
The basket holds 6 pairs: 0-0, 0-1, 0-2, 1-1, 1-2 and 2-2.
- Find every place for 2-2. There are only 2: row 1, columns 1 and 2, or row 1, columns 2 and 3.
- Both places use row 1, column 2. So that 2 must go into the 2-2 domino.
- That means row 1, column 2 cannot join the 1 below it. Put a cross between them.
- Now find every place for 1-2. With that cross, only 1 place is left: row 1, column 1 with row 2, column 1. Join them.
- Row 1, column 2 can no longer join column 1. So its 2-2 domino goes to row 1, column 3. Join them.
- Row 1, column 4 holds a 0. Its left neighbour is taken, so it joins the 0 below it. That is 0-0.
- Row 3, column 4 holds a 2. The box above it is taken, so it joins the 0 on its left. That is 0-2.
- Row 3, column 1 holds a 1. The box above it is taken, so it joins the 1 next to it. That is 1-1.
- The last 2 boxes are row 2, columns 2 and 3. They hold 1 and 0, which is 0-1. Every pair is now used once.
Beginner techniques
Only 1 place left
Look for a pair that fits in just 1 place on the board. Put it there. Pairs that fit in few places are a good start.
Only 1 partner left
Look at each box and count its free neighbours. A box in a corner, or next to taken boxes, may have just 1. Join them.
Cross pairs you have used
Once you place a pair, it cannot appear again. Cross every other place where that same pair could go.
A box every choice shares
Check every place left for a pair. If they all use the same box, that box belongs to this pair. Cross the other dominoes that box could make.
Compare 2 pairs
Pick 2 or 3 pairs you have not used yet. Look at every way to place them together. Cross a place if every way that uses it makes 2 dominoes share a box.
Common mistakes
- Using a pair twice because it is written the other way round, like 1-2 and 2-1.
- Joining 2 boxes that touch only at a corner. Dominoes join side by side.
- Leaving a box with no free neighbour. Check that every open box can still join something.
- Forgetting that doubles like 0-0 and 2-2 are part of the set.
Questions
Do I need to know the game of dominoes?
No. You only need to know that a domino covers 2 boxes side by side. There are no turns and no scores.
How many pairs are there?
With the numbers 0 to 2, the set has 6 pairs. With the numbers 0 to 4, it has 15 pairs.
What sizes are there?
Quirk has boards of 3 rows by 4 columns with the numbers 0 to 2. Bigger boards have 5 rows by 6 columns with the numbers 0 to 4.
Does every puzzle have one answer?
Yes. Each board in Quirk has exactly one answer, and you can find it without guessing.
What does a cross mean?
A cross marks 2 boxes that cannot be a domino. It helps you remember what you have ruled out.
Is it good for beginners?
Yes. The first lesson uses a tiny board with only 3 pairs. Each later lesson adds one new idea.
Related puzzles
Playing it in Quirk
Tap 2 numbers side by side to join them into a domino. Tap the same 2 again for a cross, which rules that pair out. Tap once more to clear it.
The basket lists the pairs to use. Pair choices lets you pick 2 or 3 unused pairs and see every way to place them. If you get stuck, a hint shows the next step. You can undo a move or start again.
