Map Colour Problem

The puzzle - to colour a map using at most four colours - the 4 colour problem.

Key point, no two adjacent regions have the same colour - two regions are adjacent if they share a common boundary segment (not just a point).

That only four colours are needed was the first major theorem proved by a computer! [Done by Appel and Haken].

You select the map and backtracking is used to solve it.

Press Show Solving to see how it does it - using backtracking.

Some maps can be solved using only 3 colours - you can try this.

Press Test Adjacency to see which regions are deemed to be adjacent. Here a Red region shows one region and the green regions those that are considered adjacent.

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