MAPPER = {
  "8": "eight",
  "7": "seven",
  "3": "three",
  "9": "nine",
  "5": "five",
  "4": "four",
  "6": "six",
  "2": "two",
  "1": "one"
}

#prepare the input which is a string containing new lines
def parse(input)
  data = []
  input.each_line do |line|
    data << line.chomp
  end
  data
end

def find_first_digit(line, reverse:false)
  line.length.times do |i|
    j = reverse ? line.length - 1 - i : i
    return line[j] if line[j].to_i != 0
    sub_line = line[j..-1]
    MAPPER.each do |k,v|
      return k if sub_line.start_with?(v)
    end
  end
end

# result should a single string or integer
def calculate(data)
  result = 0
  data.each_with_index do |d,i|
    first = find_first_digit(d)
    last = find_first_digit(d, reverse: true)

    num = "#{first}"+"#{last}"
    result += num.to_i
  end
  result
end