IBM Research | Ponder This | August 2015 challenges

# Ponder This

## August 2015

<<July August September>>

Ponder This Challenge:

Find a way to fold a loop of string in three-dimensional space such that all three projections will be loop-free (i.e., you won't be able to make a path from a point to itself without backtracking).

Provide your answer as a list of integer 3D coordinates, where each pair differs in exactly one coordinate.

For example, the following list is loop-free on two projections (x,z) and (y,z), but forms a loop on the third projection (x,y):
[1,1,1],[1,1,2],[2,1,2],[2,1,1],[2,2,1],[2,2,2],[1,2,2],[1,2,1],[1,1,1].

Update (18/8):

1. The 3D loop should be non-trivial, so [1,1,1],[1,2,1],[1,1,1] is not a valid solution.

We will post the names of those who submit a correct, original solution! If you don't want your name posted then please include such a statement in your submission!

We invite visitors to our website to submit an elegant solution. Send your submission to the ponder@il.ibm.com.

If you have any problems you think we might enjoy, please send them in. All replies should be sent to: ponder@il.ibm.com

Challenge: 28/07/2015 @ 12:00 PM EST
Solution: 01/09/2015 @ 12:00 PM EST
List Updated: 02/09/2015 @ 12:00 PM EST

Robert Gerbicz (28/07/2015 08:56 PM IDT)
Gregory Giecold (29/07/2015 02:12 AM IDT)
Don Dodson (29/07/2015 08:56 PM IDT)
Gary M. Gerken (30/07/2015 07:33 AM IDT)
John Tromp (30/07/2015 08:39 PM IDT)
Kang Jin Cho (01/08/2015 06:02 AM IDT)
Gregory Giecold (29/07/2015 02:12 AM IDT)
Don Dodson (29/07/2015 08:56 PM IDT)
Gary M. Gerken (30/07/2015 07:33 AM IDT)
John Tromp (30/07/2015 08:39 PM IDT)
Kang Jin Cho (01/08/2015 06:02 AM IDT)
Shirish Chinchalkar (02/08/2015 03:41 PM IDT)
Daniel Bitin (02/08/2015 11:21 PM IDT)
Harald Bögeholz (03/08/2015 01:21 AM IDT)
Liubing Yu (03/08/2015 07:53 AM IDT)
John Tromp (03/08/2015 06:23 PM IDT)
Lucas Mirelmann (05/08/2015 01:53 AM IDT)
Florian Fischer (05/08/2015 11:59 AM IDT)
Uoti Urpala (07/08/2015 12:46 AM IDT)
Graham Hemsley (07/08/2015 06:58 PM IDT)
Alexandre Gilotte (08/08/2015 12:08 AM IDT)
Francis Golding (09/08/2015 07:41 PM IDT)
Yan-Wu He (10/08/2015 12:02 PM IDT)
David Greer (10/08/2015 09:28 PM IDT)
Todd Will (11/08/2015 08:16 PM IDT)
Paolo Farinelli (12/08/2015 03:24 AM IDT)
George Stoianov (12/08/2015 04:12 PM IDT)
Joseph DeVincentis (12/08/2015 07:46 PM IDT)
Jamie Jorgensen (12/08/2015 10:46 PM IDT)
Martin Husar (13/08/2015 09:10 AM IDT)
Jesse Rearick (19/08/2015 02:53 AM IDT)
Pino Ottavio (22/08/2015 12:59 PM IDT)
Michael Rosola (22/08/2015 08:16 PM IDT)
Bradley Sherman & Mason Bouffard (28/08/2015 08:11 AM IDT)
Jim Clare (31/08/2015 03:11 AM IDT)
David Dunkley (02/09/2015 02:45 AM IDT)