length_partition.rb

# Content-Length, Worker index, Worker total count
length, index, count = ARGV.first(3).map(&method(:Integer))
slice, remainder = length.divmod(count)
min = index * slice
max = if index == (count - 1)
  # Final slice finishes on total size
  length
else
  # One less than next slice starting point
  ((index + 1) * slice) - 1
end
puts "#{min}-#{max}"