AdventOfCode-2018/day5.cr

require "./common.cr"

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

struct Char
  def inverse?(other)
    return (other != self) && (other.downcase == self.downcase)
  end
end

def react(string)
  stack = [] of Char

  string.each_char do |char|
    last_char = stack.last?
    if !last_char || !last_char.inverse? char
      stack << char
    else
      stack.pop
    end
  end

  return stack
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