Displaying empty range indices based on filled range indices

get_empty_ranges.rb

arr_size  = 100
arr = [[0,5], [20, 30], [50, 70]]

def get_ranges(arr_size, arr)
  # calculating adjacent indices
  # flatten multiple arrays in one
  arr.map!{|k, v| [get_min(k), get_max(v, arr_size)]}.flatten!
  
  # checking the occurrence of range boundaries  
  sum = arr + [0, arr_size]
  res = sum - (arr & [0, arr_size])

  # splitting the resulting array
  result = res.sort.each_slice(2).to_a
end

def get_min(item)
  item == 0 ? item : item-1
end

def get_max(item, arr_size)
  item == arr_size ? arr_size : item+1
end

puts get_ranges(arr_size, arr)