Find Missing Number from a string sequence

find_missing_no.rb

require 'pry'
=begin
x =(1..400).to_a ; deleted = x.delete(Random.rand(400)); data= x.join("")

counter = 0
prev_no = 0
offset = 0

loop do
  current_no = (data[offset..(offset+counter)]).to_i
  puts "current_no is #{current_no}"

  # considering case where we need to find numbers which jump digits
  if prev_no > current_no.to_i
    puts "incr counter to #{counter+1}"
    counter += 1
    current_no = (data[offset..(offset+counter)]).to_i
    puts "current_no is #{current_no}"
  end

  if current_no - prev_no != 1
    puts "number missing is #{prev_no+1} and current_no is #{current_no}"
    break
  end
  offset += 1+counter
  prev_no = current_no

end

=end


# if offset is 0, start from 0 of data
# if current_no is nil, there is no prev no. this is the start of the loop

# returns a sequence

def find_next_number(current_no, length, offset, data)
  puts "input is current_no #{current_no}, length #{length}, offset #{offset}, data #{data}"
  if length == nil
    length = 1
  end

  loop do
    if current_no != nil
      # assuming length has not increased or to change
      if (current_no + 1).to_s.length == current_no.to_s.length
        length = length
      else
        length +=1
      end
    end
    possible_no = (data[0..(0+length-1)]).to_i
    if !current_no.nil?
      diff = possible_no - current_no
      if diff == 1
        # happy case
      elsif diff == 2
        puts "The no. is #{current_no+1}"
        exit(2)
      else
        raise "err"
      end
    end

    begin
      find_next_number(possible_no, length, offset, data[length..-1])
    rescue => e
      length += 1
    end
    if length >= data.length
      puts "Err. could not find a seq"
      raise "errr"
    end
  end

end

data="1000 1002".gsub(" ","")
find_next_number(nil, nil, 0, data)

ismert problémák,