2025 ruby day 3, MAXIMUM_JOLTAGE

ruby/2025/3/bin/problem

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+#!/usr/bin/env ruby
+
+require "battery_bank"
+
+battery_banks = STDIN.read.chomp.split.map { |line| BatteryBank.for line }
+puts "Part 1: #{battery_banks.map(&:maximum_joltage).sum}"
+puts "Part 2: #{battery_banks.map(&:override_joltage).sum}"

ruby/2025/3/lib/battery_bank.rb

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+class BatteryBank
+  attr_reader :batteries
+
+  def initialize(batteries)
+    @batteries = batteries
+  end
+
+  def self.for(string)
+    new string.split("").map(&:to_i)
+  end
+
+  def joltage_for_batteries(num_batteries)
+    num_batteries.downto(1).reduce([[], 0]) do |acc, enabled_battery_index|
+      max_digit = batteries[(acc[1])..(-enabled_battery_index)].max
+      max_digit_index = batteries[(acc[1])..].find_index(max_digit)
+      [acc[0] + [max_digit], acc[1] + max_digit_index + 1]
+    end[0].map(&:to_s).join("").to_i
+  end
+
+  def maximum_joltage
+    joltage_for_batteries(2)
+  end
+
+  def override_joltage
+    joltage_for_batteries(12)
+  end
+end

ruby/2025/3/test/test_battery_banks.rb

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+require "minitest/autorun"
+require "battery_bank"
+
+class TestBatteryBanks < ::Minitest::Test
+  def test_maximum_joltage
+    assert_equal(98, BatteryBank.for("987654321111111").maximum_joltage)
+    assert_equal(89, BatteryBank.for("811111111111119").maximum_joltage)
+    assert_equal(78, BatteryBank.for("234234234234278").maximum_joltage)
+    assert_equal(92, BatteryBank.for("818181911112111").maximum_joltage)
+  end
+
+  def test_override_joltage
+    assert_equal(987654321111, BatteryBank.for("987654321111111").override_joltage)
+    assert_equal(811111111119, BatteryBank.for("811111111111119").override_joltage)
+    assert_equal(434234234278, BatteryBank.for("234234234234278").override_joltage)
+    assert_equal(888911112111, BatteryBank.for("818181911112111").override_joltage)
+  end
+end