AdventOfCode-2018/day5.cr

require "./common.cr"

lines = File.read("day5_input").split("\n")

def react(string)
  string = string.chars

  changed = true
  while changed
    changed = false
    i = 0
    while i < string.size - 1
      next_i = i + 1
      if string[i] != string[next_i] &&
          string[i].downcase == string[next_i].downcase
        string.delete_at i
        string.delete_at i

        i -= 1
        i = 0 if i < 0
        changed = true
      else
        i += 1
      end
    end
  end

  return string
end

puts react(lines[0]).size

pairs = {} of Tuple(Char, Char) => Int32
('a'..'z').to_a.zip(('A'..'Z').to_a).each do |pair|
  new_string = lines[0].select { |c| c != pair[0] && c != pair[1] }
  pairs[pair] = react(new_string).size
end

puts pairs.values.min