koikekeiko.rb

#!/usr/bin/ruby
#
# Usage:
# $ echo わたしたわしわたしたわ | ruby koikekeiko.rb
# 11/1
# $ echo こしたんたん | ruby koikekeiko.rb
# 3/2
#
# Calculates the "saiwaisa" of the input as defined in
# 2022年度 大学入学共通テスト 本試験 情報関係基礎
#
# Copytight 2022 by zunda <zundan at gmail.com>
#
# Permission is granted for use, copying, modification, distribution,
# and distribution of modified versions of this work as long as the
# above copyright notice is included.

class KoikeKeiko < String
  def splits(n)
    r = []
    KoikeKeiko.each_split_ary(n, self.length, []) do |ary|
      i = 0
      x = []
      ary.each do |d|
        x << KoikeKeiko.new(self[i...(i+d)])
        i += d
      end
      r << x
    end
    return r
  end

  def kaibun?
    self.reverse == self
  end

  def min_kaibun_split
    1.upto(self.length) do |s|
      if self.splits(s).map{|split| not split.find{|sub| not sub.kaibun?}}.find{|e| e}
        return s
      end
    end
  end

  def saiwaisa
    Rational(self.length, min_kaibun_split)
  end

  private
  def KoikeKeiko.each_split_ary(n, l, lefts, &block)
    if n <= 1
      yield [*lefts, l]
    else
      1.upto(l+1-n) do |x|
        KoikeKeiko.each_split_ary(n-1, l-x, lefts + [x], &block)
      end
    end
  end
end

puts KoikeKeiko.new(ARGF.read.strip).saiwaisa