■

8クイーン問題をRubyで解こうとしたが、うまくいかない。なぜだ？
疲れたのであとで考える。

#!/usr/bin/ruby -Ks
#
# 8 queen problem

$n = 8
$ini_row = 1

class Queen
  def initialize(col, neighbor)
    @row = $ini_row
    @col = col
    @neighbor = neighbor
  end

  def show
    print "　"*(@row-1), "Ｑ", "　"*($n+2-@row), "#@row, #@col\n"
  end

  def findSolution
    while @neighbor and @neighbor.canAttack(@row, @col)
      unless advance
        return false
      end
    end
    true
  end

  def canAttack(row, col)
    if (row == @row) or ((@col-col).abs == (@row-row).abs)
      return true
    end
    @neighbor and @neighbor.canAttack(row, col)
  end

  def advance
    if @row < $n
      @row += 1
      return findSolution
    end
    if @neighbor and (not @neighbor.advance)
      return false
    end
    @row = 1
    return findSolution
  end
end

lastQueen = nil
(1..$n).each do |i|
  lastQueen = Queen.new(i, lastQueen)
  lastQueen.findSolution
  lastQueen.show
end