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 Map coloring (Posted on 2015-06-05)
Imagine an island composed of several connected countries with no enclaves or exclaves. We are concerned with coloring a map of the island with as few colors as possible.

If two neighboring countries merge their border dissolves and they become the same color.

Begin with an island that can be two colored.

One or more pairs of countries merge and now the new map of the island can only be three colored.

Again, one or more countries merge and now the map of the island requires four colors.

Find the smallest number of starting countries for which this is possible as well how they are joined.

A diagram like this example of a 3 color map should be easy enough to read:

```1122
1332
1122```

 See The Solution Submitted by Jer Rating: 3.3333 (3 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
 re(2): Drawing Challenged (spoiler?) | Comment 3 of 8 |
(In reply to re: Drawing Challenged (spoiler?) by Steve Herman)

That 7 country solution is topologically equivalent to the one you described.  So you rose to the challenge of drawing your solution!

However, I was surprised to discover a 6 county solution exists.

 Posted by Jer on 2015-06-05 10:51:11

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