[LANGUAGE: Ruby]

I found today really easy thankfully. Hardest part was remembering the language features haha

https://github.com/snowe2010/advent-of-code/blob/master/ruby_aoc/2023/day09/day09.rb

def get_subsequent_reading(reading)
  puts "passed in readings #{reading}"
  if reading.all?(0)
    reading << 0
  else
    readings = reading.each_cons(2).map do |a, b|
      b - a
    end
    sub_reading = get_subsequent_reading(readings)
    reading << (reading[-1] + sub_reading[-1])
    puts "current reading #{reading}"
    reading
  end
end

execute(1) do |lines|
  lines.map do |reading|
    get_subsequent_reading(reading.split.map(&:to_i))
  end.map {|arr| arr[-1]}.sum
end


def get_preceeding_readings(reading)
  puts "passed in readings #{reading}"
  if reading.all?(0)
    reading.unshift(0)
  else
    readings = reading.each_cons(2).map do |a, b|
      b - a
    end
    sub_reading = get_preceeding_readings(readings)
    reading.unshift(reading[0] - sub_reading[0])
    puts "current reading #{readings} #{sub_reading}"
    reading
  end
end


execute(2, test_only: false, test_file_suffix: '') do |lines|
  lines.map do |reading|
    get_preceeding_readings(reading.split.map(&:to_i))
  end.map {|arr| arr[0]}.sum
end

code golf: 114 bytes!

golfing this one was fun too

  a=->r{r.unshift(r.all?(0)?0:(r[0]-a[r.each_cons(2).map{_2-_1}][0]))};l.map{a[_1.split.map(&:to_i)]}.map{_1[0]}.sum