Advent of Code, day 9

day9.rb

#!/usr/bin/env ruby

# http://adventofcode.com/day/9

require "set"

class Map

  attr_reader :cities

  def initialize   
    @distances = {}  
    @cities = Set.new
  end

  def add(city1, city2, distance)
    @distances[[city1, city2]] = distance
    @distances[[city2, city1]] = distance
    @cities << city1
    @cities << city2
  end

  def distance_between(city_pair)
    @distances.fetch(city_pair)
  end
   
end

def parse_input
  map = Map.new
  File.read("input").each_line do |line|
    raise unless line =~ /^(\w+) to (\w+) = (\d+)$/
    city1, city2, distance = $~.captures
    distance = Integer(distance)   
    map.add(city1, city2, distance)
  end
  map
end

def distance(route)
  route.each_cons(2).map do |city_pair|
    @map.distance_between(city_pair)
  end.inject(&:+)
end

@map = parse_input
distances = @map.cities.to_a.permutation.map do |route|
  distance(route)
end
puts distances.min
puts distances.max