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Here's a quick Monday morning puzzle.

You have a 14x14 rectangular game board except that the last 7 fields of the last row are missing. Each field has a lamp, and a button that toggles the lamps on that field and each of its neighbours in a cardinal direction, altogether at most five lamps. At the start, all lights are lit. Find out which buttons to push to unlight all lights.

Why I like this puzzle is:


Update: here's an example. Suppose we have a 3x4 board with the last 1 field of the last row missing. At the start, it looks like this, all lamps lit:

**** **** ***
Now we press the button on the bottom left field so three lights go off:
**** .*** ..*
then press the button above that so two lights turn back on but two lights go off:
.*** *.** *.*
now press the second button in the bottom row:
.*** **** .*.
now the button above that one:
..** ...* ...
finally press the top right button:
.... .... ...
and all the lights are off, so we've solved this small board.

In reply to Lights out puzzle by ambrus

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