allocator.rb

module Allocator
  module_function

  def allocate(inflow, weightings)
    raise 'Inflow and weightings must be present' unless [inflow, weightings].all?(&:present?)
    raise 'Inflow and weightings must be Integers' unless (weightings + [inflow]).all? { |input| input.is_a?(Integer) }
    allocations, remainders = apportion_with_remainder(inflow, weightings).transpose
    remaining_inflow = inflow - allocations.sum
    deserving_indices = remainders.each_with_index.sort_by { |remainder, i| [remainder, i] }.reverse.map { |_remainder, i| i }.first(remaining_inflow)
    allocations.each_with_index.map do |allocation, i|
      deserving_indices.include?(i) ? allocation + 1 : allocation
    end
  end

  def apportion_with_remainder(input, buckets)
    total = buckets.sum
    buckets.map do |bucket|
      (input * bucket).divmod(total)
    end
  end
end

The article explaining the logic behind the code:
https://www.betterment.com/engineering/penny-precise-allocation-functions