Project Euler Problem 1 Ruby Version

Project Euler Problem 1.rb

#単純に加算
sum = 0
(1..999).each do |i|
    if (i % 3) == 0
        sum += i
    elsif (i % 5) == 0
        sum += i
    end
end
puts sum
 
#等差数列の和
sum = 0;
#初項, 公差
[3, 5, 15].each do |a|
    n = 999 / a #項数
    l = n * a;  #末項 a＋(n－1)d
 
    case a
        when 3, 5
            sum += ((a + l) * n / 2)
        else
            sum -= ((a + l) * n / 2)
    end
end
puts sum