Knight’s Tour Problem [backtracking, ruby]

knights_tour.rb

# A knight’s tour is a sequence of moves of a knight on a chessboard such that 
# the knight visits every square only once. If the knight ends on a square that 
# is one knight’s move from the beginning square (so that it could tour the board 
# again immediately, following the same path), the tour is closed, otherwise it is open.

class KnightTour
  def initialize(n)
    @n = n
    @path = 0
    @board = Array.new(n) { Array.new(n, 0) }
  end

  def solve
    if find_path(0, 0, 0) then print_board else puts "NO PATH FOUND" end
  end

  def find_path(row, col, index)
    return false if @board[row][col] != 0
    @path += 1
    @board[row][col] = @path
    return true if index == @n*@n-1
    variations = [[2,1],[2,-1],[1,2],[1,-2],[-1,2],[-1,-2],[-2,1],[-2,-1]]
    variations.each do |var_row, var_col|
      if can_move?(row+var_row, col+var_col)
        return true if find_path(row+var_row, col+var_col, index+1)
      end
    end
    @board[row][col] = 0
    @path -= 1
    false
  end

  def can_move?(row, col)
    row.between?(0,@n-1) and col.between?(0,@n-1)
  end

  def print_board
    puts "Board:"
    @board.each do |row|
      row.each do |value|
        print value < 10 ? " #{value} " : "#{value} "
      end
      puts
    end
  end

end

n = 6
i = KnightTour.new(n)
i.solve