My general solution (nxn dots, 2*n-2 stright lines):http://www.scribd.com/doc/133494020/Extended-9-dots-puzzle-to-nx2-dots
I could not expect a better solution!!! Bravo Marco!!You have already answered to my next riddle!! i was going to post my next riddle about n x n dots. Bravo!! I think you fit in this blog! And i believe you know lots of riddles!write us the riddle or puzzle you liked most ever.
Hehehhehe... many thanks!Unfortunately I don't know a lot of riddles, I've just created a few riddles/questions by myself for the ebook I linked in my previous post (most of them are number theory related problems).BTW this blog is very nice, I wish you the best :)P.S.There is another interesting result related to this puzzle... I typed it as a comment here: http://oeis.org/A058992. To be short: the gossip problem and the nxn dots puzzle are the same thing (looking at it from a mathematical perspective), to solve a nxn dots puzzle you need 2n-2 stright lines and, to interact with any people in a set of n, you need 2n-2 "calls" as well!
I would solve this by drawing 4 lines to cover the "frame", thus converting it to the classic 3x3 points 4 lines problem.Similar solution can be used for every n>3.
5 From the top left spot down the left slightly angled and very long so I can come straight back up into the second to left column and continue like that.
You only need 1 line, it just needs to be very thick. :-)
Final proof by me... thinking inside and outside the box and the square "spiral method":http://www.scribd.com/doc/137604469/Extended-9-Dots-Puzzle-final-proof-general-solving-methodFor nay n>5, you can solve any nxn puzzle INSIDE the box (using the square spiral method).