Chinese checkers solver written in Crystal

chinese_checkers.cr

Directions = [:up, :down, :left, :right]

class Board
  getter :cells

  def initialize
    @cells = [
      ['x', 'x', ' ', 'o', ' ', 'x', 'x'],
      ['x', 'x', ' ', 'o', ' ', 'x', 'x'],
      [' ', ' ', 'o', 'o', 'o', ' ', ' '],
      ['o', 'o', 'o', ' ', 'o', 'o', 'o'],
      [' ', ' ', 'o', 'o', 'o', ' ', ' '],
      ['x', 'x', ' ', 'o', ' ', 'x', 'x'],
      ['x', 'x', ' ', 'o', ' ', 'x', 'x'],
    ]
  end

  def initialize(@cells)
  end

  def can_move?(row, col, direction)
    return false unless @cells[row][col] == 'o'

    case direction
    when :up
      row >= 2 && @cells[row - 1][col] == 'o' && @cells[row - 2][col] == ' '
    when :down
      row <= 4 && @cells[row + 1][col] == 'o' && @cells[row + 2][col] == ' '
    when :left
      col >= 2 && @cells[row][col - 1] == 'o' && @cells[row][col - 2] == ' '
    when :right
      col <= 4 && @cells[row][col + 1] == 'o' && @cells[row][col + 2] == ' '
    else
      raise "Unknown direction: #{direction}"
    end
  end

  def move(row, col, direction)
    new_cells = @cells.clone
    case direction
    when :up
      new_cells[row][col] = ' '
      new_cells[row - 1][col] = ' '
      new_cells[row - 2][col] = 'o'
    when :down
      new_cells[row][col] = ' '
      new_cells[row + 1][col] = ' '
      new_cells[row + 2][col] = 'o'
    when :left
      new_cells[row][col] = ' '
      new_cells[row][col - 1] = ' '
      new_cells[row][col - 2] = 'o'
    when :right
      new_cells[row][col] = ' '
      new_cells[row][col + 1] = ' '
      new_cells[row][col + 2] = 'o'
    else
      raise "Unknown direction: #{direction}"
    end
    Board.new(new_cells)
  end

  def solved?
    @cells.each_with_index do |row, row_index|
      row.each_with_index do |cell, col_index|
        if row_index == 3 && col_index == 3
          return false unless cell == 'o'
        else
          return false if cell == 'o'
        end
      end
    end
    true
  end

  def to_s
    to_s(-1, -1)
  end

  def to_s(highlight_row, highlight_col)
    String.build do |str|
      str << "---------"
      @cells.each_with_index do |row, row_index|
        str << "\n|"
        row.each_with_index do |cell, col_index|
          if row_index == highlight_row && col_index == highlight_col
            str << "\033[1;32m#{cell}\033[0m"
          else
            str << cell
          end
        end
        str << "|"
      end
      str << "\n---------"
    end
  end
end

class Solver
  getter :board
  getter :row
  getter :col
  getter :direction
  getter :next_board
  getter :next_solver

  def initialize(@board = Board.new)
    @row = -1
    @col = -1
    @direction = :none
  end

  def solve
    7.times do |row|
      7.times do |col|
        Directions.each do |direction|
          if @board.can_move?(row, col, direction)
            next_board = @board.move(row, col, direction)
            if next_board.solved? || (@next_solver = Solver.new(next_board)).solve
              @next_board = next_board
              @row = row
              @col = col
              @direction = direction
              return true
            end
          end
        end
      end
    end
    @next_solver = nil
    false
  end

  def to_s
    board.to_s row, col
  end
end

solver = Solver.new
if solver.solve
  puts "The solution is..."
  current_solver = solver
  while current_solver
    puts
    if current_solver.next_solver
      puts "Move #{current_solver.direction}"
      puts current_solver
      current_board = current_solver.next_board
    else
      puts "Finally..."
      puts current_board
    end
    current_solver = current_solver.next_solver
  end
else
  puts "No solution : -("
end