年月 (from, to) のデータから、のべ年数を計算する

data.txt

20143 20149
20162 20175
20162 20164
20165 20166
20169 201611
20172 20175
20181 20192
20194 20195
20203 20208
202011 20222
20227 202211

solver.rb

require 'active_support'
require 'active_support/core_ext'
require 'date'

date_matcher = /^(^\d{,4})(\d+?)$/ # 年・月で区切る
data =
  File.read(File.join(__dir__, 'data.txt'))
      .lines
      .map(&:chomp)
      .map { |x| x.split.map { |y| y.match(date_matcher).captures.map(&:to_i) } }

days_array =
  data.map do |from, to|
    from_date = Date.new(*from)
    to_date = Date.new(*to)

    (to_date - from_date).to_i
  end

pp days_array.sum.days.in_years.to_i # => 5