## LightsOut Tutorial

LightsOut is a puzzle where you are given a grid of cells, or lights, with
some dark and others light. You must turn them all off by clicking on the
cells. Each click toggles that cell and each of its immediate neighbors.

Play our LightsOut now or read on for a method
to solve these puzzles.

## How To Solve LightsOut Puzzles

All valid LightsOut puzzles can be solved without clicking on any cell
twice. This is because clikcing on a cell twice is the same as not clicking
it at all.

### Chase The Lights

The easiest way to solve LightsOut puzzles is to use a method called Chase
The Lights. Starting with the second row, click on every cell that has a light
on in the row above it. This will turn off all the lights in that row.
Continue with each successive row until the only remaining lights are in the
final row.

### Pattern Lookup

Now that you only have lights on in the final row, use the lookup table
below and find the pattern of lights. This will tell you which lights to
click in the top row. When you chase the lights this time, the bottom row
will end up dark, just like the rest of the puzzle.

Bottom Row Lights | Top Row Clicks |

..*** | ...+. |

.*.*. | .+..+ |

.**.* | +.... |

*...* | ...++ |

*.**. | ....+ |

**.** | ..+.. |

***.. | .+... |

For a 9x9 puzzle, you will either end up with a dark bottom row, or *.*.*.*.*
as your pattern. If you have the latter, click the top left cell, and chase it
to turn out all the lights.

### Fewest Moves

Obviously this method will often result in more moves than necessary, as
you will sometimes end up clicking a cell twice as you chase the lights two
times. To figure out the fewest possible moves, take the click pattern for
the top row, and start with that on the original puzzle. This time you will
only need to chase the lights once.

This still might not result in the fewest possible moves, as chasing the
following top row click patterns result in no change to a 5x5 puzzle:

.+++.
+.+.+
++.++

So applying one of these top row click patterns before you start the puzzle
may result in fewer clicks.

For a 9x9 puzzle, there are even more combinations of top row clicks that
don't change the puzzle win chased to the bottom. Clicking any even numbered
cell in the top row, or clicking any two odd numbered cells will do this, as
will any combination of such clicks. So, while a 9x9 puzzle is fairly easy to
solve, it can be quite difficult to solve it in the fewest possible clicks.