What is the minimum number of strokes to reproduce the drawing below without lifting up the pencil from the paper (no tricks at all), and without passing over a line segment (or part of it) already drawn? You may begin and end wherever you like, and line segments may cross each other, but only as intersections.

Note: a new stroke occurs when a line type ceased because you have to stop and change direction.

14 strokes:

BCLGJNBKKOADFMD

This is provably the minimum.


The theoretical minimum is 13 strokes, since there are 12 lines and 1 circle.  But this is not possible because if each line is traced without breaks, then we would have to lift our pencil to get from (for instance) line KO to line LC.  Therefore, at least one line must be broken.

The reason this solution works is because KA is broken in two: segment KB and DA.  Note that these two segments overlap.

Posted by Tristan on 2005-11-25 20:51:11