Create a game board

You can use the random_board() function to initialize a new Lights Out game with a random configuration of lights. The generated board is guaranteed to be solvable. The first argument to the function is the board dimensions (number of rows and columns), which is restricted to be either 3, 5, 7, or 9.

library(lightsout)
random1 <- random_board(3)
random1

#> Lights Out 3x3 board
#> Game mode: classic 
#> 
#>  0 0 1
#>  1 1 1
#>  1 1 0
#>  

random2 <- random_board(5)
random2

#> Lights Out 5x5 board
#> Game mode: classic 
#> 
#>  0 0 0 0 1
#>  1 0 1 1 0
#>  1 1 1 1 1
#>  0 0 0 0 0
#>  0 0 1 1 0
#>  

You can also use the new_board() function to create a new board if you want to provide your own defined set of lights. The first argument is either a matrix or a vector of the lights, with all values being either 0 (light off) or 1 (light on). If a vector is provided, then it is read row-by-row rather than column-by-column.

lights_vector <- c(0, 0, 0,
                   0, 1, 0,
                   1, 1, 1)
board1 <- new_board(lights_vector)
board1

#> Lights Out 3x3 board
#> Game mode: classic 
#> 
#>  0 0 0
#>  0 1 0
#>  1 1 1
#>  

Any board generated by random_board() is guaranteed to be solvable, but since we defined this board ourselves, it’s a good idea to make sure it’s solvable before attempting to play it.

is_solvable(board1)

#> [1] TRUE

Press a light

Pressing a light is done with the play() function. Pressing a light will cause that light and all its adjacent lights to toggle (in classic mode, which is the default). All the coordinates in lightsout are treated as (row,column). Let’s press the light at (2,3) - row 2, column 3

# Press light at (2,3)
played <- play(board1, 2, 3)
played

#> Lights Out 3x3 board
#> Game mode: classic 
#> 
#>  0 0 1
#>  0 0 1
#>  1 1 0
#>  

Notice how the light at (2,3) and its 4 neighbours are flipped.

If you want to play the non-classic game mode, where pressing a light toggles the entire row and column, then use the classic = FALSE argument of either new_board() or random_board(). To demonstrate, here is the same board initialized as non-classic mode, with the same light being pressed.

# Press light at (2,3) in non-classic mode
new_board(lights_vector, classic = FALSE) %>% play(2, 3)

#> Lights Out 3x3 board
#> Game mode: entire row/column 
#> 
#>  0 0 1
#>  1 0 1
#>  1 1 0
#>  

Note that this specific board does not actually have a solution in non-classic mode, which means that no combination of lights being pressed will result in all lights being off:

new_board(lights_vector, classic = FALSE) %>% is_solvable()

#> [1] FALSE

Notice also that lightsout works well with the %>% operator that allows you to easily chain calls.

Press multiple lights

By chaining calls, you can press multiple lights easily one after the other:

# Press light at (2,3) and then (1,2)
board1 %>% play(2, 3) %>% play(1, 2)

#> Lights Out 3x3 board
#> Game mode: classic 
#> 
#>  1 1 0
#>  0 1 1
#>  1 1 0
#>  

By the way, when pressing multiple lights, the order does not matter. Pressing y after x will always have the same result as pressing x after y.

If you want to press multiple lights in one call, you can pass a vector of row numbers and a vector of column numbers instead of a single row and column. The previous chain of presses can also be achieved with:

# Press light at (2,3) and (1,2)
board1 %>% play(c(2, 1), c(3, 2))

#> Lights Out 3x3 board
#> Game mode: classic 
#> 
#>  1 1 0
#>  0 1 1
#>  1 1 0
#>  

Another way to press many lights with one call is to use a matrix instead of rows and columns. The matrix must have the same dimensions as the board, and every position in the matrix with a value of 1 means that the light in that position will be pressed.

# Press light at (2,3) and (1,2)
board1 %>% play(matrix = matrix(nrow = 3, byrow = TRUE,
                                c(0, 1, 0,
                                  0, 0, 1,
                                  0, 0, 0)))

#> Lights Out 3x3 board
#> Game mode: classic 
#> 
#>  1 1 0
#>  0 1 1
#>  1 1 0
#>  

Now let’s try to actually solve the board. The board we have is actually super easy - it should be obvious that a single press at (3,2) will turn off all the lights.

play(board1, 3, 2)

#> Good job, you won!

If you have a more complex board, it will generally require many more presses and will not be as trivial to solve. Let’s create a random board of size 5.

bigboard <- random_board(size = 5)
bigboard

#> Lights Out 5x5 board
#> Game mode: classic 
#> 
#>  1 0 0 0 1
#>  1 1 0 0 1
#>  1 1 0 1 1
#>  0 0 0 0 1
#>  1 0 0 1 0
#>  

This one isn’t so simple, is it? You can try playing with it for a bit.

Get the solution

If you want to see the solution to a board, use the solve_board() function:

solution <- solve_board(bigboard)
solution

#> 
#>  0 1 1 1 0
#>  0 0 1 0 0
#>  1 1 0 0 1
#>  1 1 0 0 0
#>  1 1 1 0 0
#>  

The solution is a matrix with the same dimensions as the board, with the values of 1 representing the lights that need to be pressed. We can verify that the solution does indeed solve the current board:

bigboard %>% play(matrix = solution)

#> Good job, you won!