aoc2025/day_05/2.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

class Main
  def run
    ranges = []
    $stdin.each_line do |line|
      arr = line.chomp.split("-").map(&:to_i)
      if arr.size == 2
        ranges << (arr[0]..arr[1])
      end
    end

    # Sort ranges by starting point
    # This prevents having to check all previous ranges for every new range
    ranges.sort_by!(&:begin)

    valid_id_ranges = []
    ranges.each do |r|
      valid_id_ranges.each do |vr|
        if (
            # r starts inside vr
            r.begin >= vr.begin && r.begin <= vr.end) ||
            # r ends inside vr
            (r.end >= vr.begin && r.end <= vr.end) ||
            # vr starts inside r
            (vr.begin >= r.begin && vr.begin <= r.end) ||
            # vr ends inside r
            (vr.end >= r.begin && vr.end <= r.end)
          # Merge ranges
          r = ([r.begin, vr.begin].min..[r.end, vr.end].max)
          valid_id_ranges.delete(vr)
        end
      end
      valid_id_ranges << r
    end

    @total = 0
    valid_id_ranges.each do |r|
      @total += (r.end - r.begin + 1)
    end

    puts @total
  end
end

Main.new.run