perplexus.info :: General : Lights Out!

Lights Out! (Posted on 2003-11-02)

Imagine there is a 5x5 grid of lights, and only the middle light in the grid is on.

The lights are wired such that when you flip the switch for one light (from on to off or off to on) the others right next to it (not diagonally) flip as well.

Using this weird wiring of lights, what is the fewest number of switch changes it takes to turn all the lights off, and which lights should you switch? (Assume all the switches work in the manner explained, and there is 1 switch for each of the lights.)

Submitted by Gamer

Rating: 4.0000 (2 votes)

Solution: (Hide)

Charlie explains the solution as follows:

The following arrangement of flipped switches (1 = flipped, 0 = not flipped) will turn off the center light while keeping or returning off the other lights:

0 0 0 1 1
0 0 1 0 0
0 1 1 0 1
1 0 0 0 1
1 0 1 1 0

This arrangement's rotations/reflections are the 3 other solutions.

Comments: ( You must be logged in to post comments.)

Subject	Author	Date
Puzzle Thoughts	K Sengupta	2022-05-19 00:12:08
re: well one way	Gamer	2003-11-07 07:10:13
re: Lights On!	Charlie	2003-11-06 17:29:55
Lights On!	wonshot	2003-11-06 12:24:16
well one way	Joe C	2003-11-06 07:54:52
re(3): Brute Force	Charlie	2003-11-04 00:39:10
re(2): Brute Force	Charlie	2003-11-03 23:18:07
re: Brute Force	Tristan	2003-11-03 18:58:17
Oh hell nevermind.	Choop	2003-11-03 01:17:29
ANSWER HERE.	Choop	2003-11-03 01:12:10
real-world method	Lee	2003-11-02 23:32:30
No Subject	Lee	2003-11-02 23:28:45
re: Brute Force	Charlie	2003-11-02 20:29:10
re(2): Brute Force	Charlie	2003-11-02 20:19:59
re: Brute Force	rerun141	2003-11-02 19:49:19
Brute Force	Charlie	2003-11-02 18:01:31
re(3): First steps to proof	Victor Zapana	2003-11-02 17:16:50
re(2): First steps to proof	rerun141	2003-11-02 16:36:36
re: First steps to proof	Victor Zapana	2003-11-02 16:16:31
First steps to proof	Tristan	2003-11-02 15:56:24
possibly impossible	Victor Zapana	2003-11-02 14:05:48
re: Solution or impossible	Victor Zapana	2003-11-02 13:42:26
Solution or impossible	Gamer	2003-11-02 11:00:45
re: stuck lol	rerun141	2003-11-02 10:48:03
stuck lol	Victor Zapana	2003-11-02 09:14:54
re: question to gamer	Victor Zapana	2003-11-02 09:00:38
question to gamer	Victor Zapana	2003-11-02 08:57:31

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