Discussion on: Advent of Code 2020 Solution Megathread - Day 2: Password Philosophy

require 'benchmark'

class PasswordPolicy
  def self.from_line(line)
    length, char, password = line.split(' ')
    first, second = length.split('-').map(&:to_i)
    char = char.delete(':')

    PasswordPolicy.new(positions: [first - 1, second - 1], char: char, password: password)
  end

  def initialize(positions:, char:, password:)
    self.positions = positions
    self.char = char
    self.password = password
  end

  def valid?
    positions.count { |i| password[i] == char } == 1
  end

  private

  attr_accessor :positions, :char, :password
end

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

valids = 0

Benchmark.bmbm do |x|
  x.report do
    valids = lines.count do |line|
      PasswordPolicy.from_line(line).valid?
    end
  end
end

puts valids

entries = File.readlines('input.txt').map do |line|
  positions, char, password = line.split
  left, right = positions.split(?-).map(&:to_i)
  [left, right, char.first, password.chomp]
}

puts entries.count do |left, right, char, password|
  (password[left - 1] == char) != (password[right - 1] == char)
}