Question

I’m trying to figure out how to select an array value if it is adjacent to a filled array value and is empty.

So let’s say the grid the array references is laid out like so.

 a1,a2,a3,
 b1,b2,b3,
 c1,c2,c3

If a1 holds an X the grid will now look like so.

 X,a2,a3,
 b1,b2,b3,
 c1,c2,c3

I want the method to be able to find the adjacent array values, in this case, a2, b1 and b2.

But in this next case where O holds the center value.

 X,a2,a3,
 b1,O,b3,
 c1,c2,c3  

…the method would select a2, b1

Can anyone provide a solution or a tip?

This is a simple tic-tac-toe grid

Here is a look at the class where the grid lives.

class Board
attr_reader :grid

def initialize(cell_value = " ")
  @grid = {
    a1: cell_value, a2: cell_value, a3: cell_value,
    b1: cell_value, b2: cell_value, b3: cell_value,
    c1: cell_value, c2: cell_value, c3: cell_value
  }
end

def printgrid
  board = "\n"
  board << "a #{@grid[:a1]}|#{@grid[:a2]}|#{@grid[:a3]} \n"
  board << "----------\n"
  board << "b #{@grid[:b1]}|#{@grid[:b2]}|#{@grid[:b3]} \n"
  board << "----------\n"
  board << "c #{@grid[:c1]}|#{@grid[:c2]}|#{@grid[:c3]} \n"
  board << "----------\n"
  board << "  1 2 3\n"
end

def space_taken?(cell_location)
  cell_value = cell_location
  @grid[cell_value] != " "
end
end

Answer 1

You could implement a method to determine if a cell is next to an X:

def next_to_x?(cell_location)
  case cell_location
  when :a1
    @grid[:a2] == 'X' or @grid[:b1] == 'X' or @grid[:b2] == 'X'
  when :a2
    @grid[:a1] == 'X' or @grid[:a3] == 'X' or @grid[:b1] == 'X' or @grid[:b2] == 'X' or @grid[:b3] == 'X'
  # ...
  end
end

Then, to find all cells that are both empty and next to an X:

[:a1, :a2, :a3, :b1, :b2, :b3, :c1, :c2, :c3].find_all { |cell_location|
  !space_taken(cell_location) and next_to_x?(cell_location)
}