aoc2025/day_06/1.rb

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

class Main
  def run
    problems = Hash.new(0)
    $stdin.each_line do |line|
      arr = line.chomp.split.map do |part|
        if /^\d+$/.match?(part)
          part.to_i
        else
          part.to_sym
        end
      end.compact

      arr.each_with_index do |part, idx|
        problems[idx] = [] unless problems.key?(idx)
        problems[idx] << part
      end
    end

    @sum = 0
    problems.each do |_, parts|
      @sum += recurse(parts[..-2], parts.last)
    end

    puts @sum
  end

  def recurse(nums, op)
    return nums.first if nums.size == 1

    num1, num2 = nums.shift(2)

    case op
    when :+
      nums.unshift(num1 + num2)
    when :-
      nums.unshift(num1 - num2)
    when :*
      nums.unshift(num1 * num2)
    when :/
      if num2 == 0
        raise "Division by zero"
      end
      nums.unshift(num1 / num2)
    end

    recurse(nums, op)
  end
end

Main.new.run