Day7b.rb

class Integer
  def sumtorial
    (0..self).sum
  end
end

def cost(counts, x0)
  counts.sum {|x, n| (x0 - x).abs.sumtorial * n}
end

count_by_pos = Hash.new(0)

gets.chomp.split(',').map(&:to_i).each do |x|
  count_by_pos[x] += 1
end

rg = count_by_pos.keys.min..count_by_pos.keys.max
optimal = rg.map {|x| cost(count_by_pos, x)}.min
print optimal