inject便利だ。 # 等差数列 def f(a, d, c) c.times.map{|i| a + (d * i)} end p f(1, 1, 5) # 等比数列 def f2(a, r, c) c.times.map{|i| (a * r **i)} end p f2(1, 3, 5) # 等比数列 DP ver def f3(a, r, c) c.times.inject([]){|res, _| res << (res.last…