gacha.rb

ITEMS_BASIC = [
  [:R, 82],
  [:SR, 15],
  [:SSR, 3],
]

ITEMS_SPECIAL = [
  [:SR, 97],
  [:SSR, 3],
]

def gacha(items)
  total = items.map(&:last).reduce(:+)
  current = Random.rand(total)
  items.find {|(_, weight)| (current -= weight) <= 0 }[0]
end

result = Array.new(9) { gacha(ITEMS_BASIC) }

if result.include?(:SR) || result.include?(:SSR)
  result << gacha(ITEMS_BASIC)
else
  result << gacha(ITEMS_SPECIAL)
end

puts "[#{result.join(', ')}]"
puts result.include?(:SSR) ? "SSRが#{result.count {|i| i == :SSR}}つあります！！！" : "SSRはありませんでした。"