array = [211, 200, 200, 200, 200, 200, 200, 200, 200, 200, 200, 200]

array = [211, 200, 199, 198, 197, 196 ... ]

def change_em(arr)
  dup_indices = arr.each_index.group_by { |i| arr[i] }.values.flat_map { |a| a.drop(1) }
  puts "dup_indices = #{dup_indices}"
  last = arr.first + 1
  arr.each_index.map { |i| last = dup_indices.include?(i) ? last-1 : arr[i] }
end

change_em [10, 8, 5, 5, 7]
  #=> dup_indices = [3]
  #=> [10, 8, 5, 4, 7]
change_em [10, 8, 7, 5, 5]
  #=> dup_indices = [4]
  #=> [10, 8, 7, 5, 4]
change_em [211, 200, 200, 200, 200, 200, 200, 200, 200, 200, 200, 200, 196]
  #=> dup_indices = [2, 3, 4, 5, 6, 7, 8, 9, 10, 11]
  #=> [211, 200, 199, 198, 197, 196, 195, 194, 193, 192, 191, 190, 196]

def f(arr, dups = [])
  return deduct_dups(dups) if arr.empty?
  if arr[0] != arr[1] # Not duplicates
    if dups.empty? # No duplicates to insert
      [arr[0]] + f(arr[1..-1])
    else # Insert duplicates
      deduct_dups(dups) + f(arr[1..-1])
    end
  else # Duplicate found, add the first element to the dup array
    f(arr[1..-1], dups.push(arr[0]))
  end
end

def deduct_dups(dups)
  return [] if dups.empty?
  (dups.first - dups.length..dups.first).to_a.reverse
end

p f [211, 200, 200, 200, 200, 200, 200, 200, 200, 200, 200, 200]
# => [211, 200, 199, 198, 197, 196, 195, 194, 193, 192, 191, 190]

p f [10, 8, 5, 5, 7].sort.reverse
# => [10, 8, 5, 4, 7]

p f [9, 6, 6, 5, 5, 4, 4, 3, 3, 3, 2, 2, 1].sort.reverse
# => [9, 6, 5, 5, 4, 4, 3, 3, 2, 1, 2, 1, 1]