# How To Solve Domino Puzzles

The Domino puzzle is based on the well-known game played with rectangular tiles.

The puzzle consists of a rectangular grid, with each cell occupied by a single digit number. The grid represents a set of domino pieces in a rectangular array.

Each domino piece is a rectangle containing two ends. Each end has a number. Depending on the size of the grid (and therefore the puzzle's difficulty), each end can contain a number from 0 to 9. The puzzle will specify the number range for that puzzle. Smaller puzzles may include numbers from 0 to 3.

There are no duplicate dominos in any puzzle. All the dominos in the array are contained in the puzzle. For example, if the puzzle uses dominos from 0-0 to 3-3, you can expect to find all the following ten pieces in the puzzle:

0-0, 0-1, 0-2, 0-3, 1-1, 1-2, 1-3, 2-2, 2-3, 3-3.

Note that a piece may be flipped, so the 0-1 and 1-0 are the same single piece.

To solve the puzzle, outline (draw a border around) pairs of adjacent numbers so that every piece of the domino set is revealed. The pieces can be laid out vertically or horizontally. No number can be a part of two pieces - so there is no overlapping. ## Domino Puzzle

Here is a typical Domino puzzle grid. The grid size can be smaller or larger and varies in difficulty.

This puzzle requires that you find the dominos from 0-0 to 5-5 (notice that the largest number in the grid is 5). The dominos can be laid out vertically or horizontally. ## Domino Solution

The solution to the puzzle is shown here. Notice that each domino piece is outlined with a rectangle. Each piece contains only two numbers, and there are no overlapping pieces. All the dominos from 0-0 to 5-5 are present (0-0, 0-1, 0-2, etc.).

### Some Common Strategies

• Look for dominos that can only be placed in one place in the grid. For example, in the sample puzzle above, notice only one area contains 0-0 (5th row), so this must be that domino. Contrast this to the two 4-4 combinations in rows one and three. In this case, we do not yet know which is correct.

• Check the digits in the four corners. When the two adjacent digits (beside and above/below) are the same, you know that must be the domino for those two numbers. For example, there is a 2 in the top right corner of the sample puzzle with a 0 to the left and below it. The 0-2 domino must be in that corner and cannot exist in any other place in the puzzle, such as in column six or row five.