nums is a list, so Enum.at has an O(N) access time. Switching nums to a map:
faster_nums =
nums
|> Enum.sort()
|> Enum.with_index()
|> Map.new(fn {value, index} -> {index, value} end)
and using Map.get or the Access protocol:
faster_nums[a] # instead of Enum.at(nums, a)
should do the trick, although that would be far from perfect. You can consider using Erlang’s array.
