Lights Out is a grid-based puzzle where each cell has two states: on/off. You can swap the state of any cell, but when you do so, the adjacent cells (horizontally or vertically) are swapped as well. Given initial the grid with random states, the objective is to set all cells to off state.
However, I've never been able to develop a strategy of how to solve (by hand) this type of puzzle. Usually I end up switching cells at random. What kinds of strategy are available for solving this game?
There are many variations of this puzzle, but I'm only interested in the classic one.
This puzzle is available in many grid sizes. It's desirable, but not required, that the proposed strategies work on all grid sizes.
My usual (and flawed) strategy is trying to clear row after row, from the top to the bottom. Unfortunately, I end up unable to clear the last row, and then I just start swapping cells at random, or just ragequit altogether.
There is an open-source and multi-platform implementation called flip as part of Simon Tatham's Portable Puzzle Collection.