### Random Post

### Recent Posts

### Recent Comments

### Archives

### Categories

- article (11)
- enigma (1,367)
- misc (4)
- project euler (2)
- puzzle (90)
- puzzle# (48)
- site news (58)
- tantalizer (94)
- teaser (7)

### Site Stats

- 233,130 hits

Programming Enigma Puzzles

25 June 2014

Posted by on **From New Scientist #2472, 6th November 2004**

From a full set of dominoes, I have taken just those that have a 1, 2, 3 or 4 at each end. I then arranged them into a rectangle, as shown, with each domino occupying two adjacent squares. The numbers are the product of the entries in that row or column. Just four dominoes are horizontal.

Which ones?

[enigma1314]

%d bloggers like this:

This Python program tries to fit the dominoes into the grid recursively, checking the products as rows and columns are completed. It runs in 3.2s.

Solution:The four horizontal dominoes are: 1-2, 2-2, 3-4 and 4-4.Here is a diagram of the layout of the dominoes (horizontal dominoes are shown in red, vertical dominoes in blue):

There are two other ways to lay out the dominoes which give the same numerical grid, but each of them has six horizontal dominoes: