# 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.