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

ids = File.readlines('input.txt')

twos = 0
threes = 0

ids.each do |id|
  counts = id.chars.each_with_object(Hash.new(0)) { |e, h| h[e] += 1 }
  twos += 1 if counts.any? { |_k, v| v == 2 }
  threes += 1 if counts.any? { |_k, v| v == 3 }
end

puts "Part 1: #{twos * threes}"

def check(a, b)
  diff_indices = a.each_char.with_index.reject { |c, i| c == b[i] }.map(&:last)
  $diff_i = diff_indices.first if diff_indices.size == 1
end

puts "Part 2: #{ids.combination(2).find { |c| check *c }.first.tap { |s| s.slice! $diff_i }}"