In ruby, this is most easily achieved with: result = input.each_cons(3).map do |left, _, right| left + right end This maps over consecutive th

In ruby, this is most easily achieved with: result = input.each_cons(3).map do |left, _, right| left + right end This maps over consecutive three-tuples in `input` and returns empty array for `len(input) < 3`. Edit: nevermind, boundary conditions are still special cases.