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I came across this question in FB. I tried to solve but unable to get the answer for it. Feeling so demotivated. This is the question:

I need to turn the whole board WHITE.
Rules of the game:
1.When you select a square, the color of that square switches (from Black to White or vice-versa).
2.In the same move, the colors of the squares at the TOP, LEFT, RIGHT, BOTTOM of the selected square, if available on the board, switch (from Black to White or vice-versa) as well. Which squares should I select to win the game.

enter image description here

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    $\begingroup$ Are you sure that question doesn't say to turn all the written numbers white.. :D $\endgroup$
    – manshu
    Mar 13, 2016 at 16:03
  • $\begingroup$ It says to turn the board white! It should be covered full of white $\endgroup$
    – Born2Code
    Mar 13, 2016 at 16:28

2 Answers 2

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This kind of puzzle is commonly referred to as "lights out", after a board game by that name. I googled that phrase and came upon a solver at http://www.ueda.info.waseda.ac.jp/~n-kato/lightsout/. So I can't take credit for the answer but it's pretty simple:

1, 3, 7, 9

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The answer to that puzzle is the following moves:

  1. First select the square number 5 to turn all the board to black.
  2. Then select all the squares positionned in a corner which are 1, 3, 7 and 9. We obtain like that the inverse of the initial board.
  3. Then simply select the square number 5 and all the board is white.
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    $\begingroup$ But the 5 in step 1 and 3 cancel eachother out, so you don't need to select 5 in this set up. $\endgroup$
    – Klyzx
    Mar 15, 2016 at 16:30

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