main.rb

require "pry"
require "./city.rb"
require "./tour.rb"

srand(0)

cities8, cities10, cities100, cities1000 =
  [8, 10, 100, 1000].map { |n|
    City.random_cities(n)
  }

def all_tours(cities)
  start = cities.first
  (cities - [start]).permutation.map { |permutation|
    Tour.new([start] + permutation)
  }
end

def exact_tsp(cities)
  shortest(all_tours(cities))
end

def shortest(tours)
  tours.min_by(&:distance)
end

def greedy_tsp(cities, start = nil)
  start ||= cities.first
  tour = [start]
  unvisited = cities - [start]
  loop do
    break unless unvisited.any?
    c = nearest_neighbor(tour[-1], unvisited)
    tour.push(c)
    unvisited.delete(c)
  end

  Tour.new(tour)
end

def all_greedy_tsp(cities)
  shortest(
    cities.each_with_index.map { |city, index|
      greedy_tsp(cities, city)
    }
  )
end

def nearest_neighbor(a, cities)
  cities.min_by { |city|
    City.distance(a, city)
  }
end



def greedy_exact_end_tsp(cities, start = nil, end_size = 8)
  start ||= cities.first
  tour = [start]
  unvisited = cities - [start]
  loop do
    break unless unvisited.length > end_size
    c = nearest_neighbor(tour[-1], unvisited)
    tour.push(c)
    unvisited.delete(c)
  end

  best = shortest(
    unvisited.permutation.map { |permutation|
      Tour.new([tour[0], tour[-1]] + permutation)
    }
  )
  Tour.new(tour + best.cities[2..-1])
end

def greedy_bi_tsp(cities, start_size=12, end_size=6)
  starts = cities.sample([cities.length, start_size].min)
  shortest(
    starts.map { |start|
      greedy_exact_end_tsp(cities, start, end_size)
    }
  )
end

=begin
exact = exact_tsp(cities10)
puts exact.distance
exact.plot("exact")
=end

greedy = greedy_tsp(cities100)
puts greedy.distance
greedy.plot("greedy")

all_greedy = all_greedy_tsp(cities100)
puts all_greedy.distance
all_greedy.plot("all_greedy")

greedy_exact_end = greedy_exact_end_tsp(cities100)
puts greedy_exact_end.distance
greedy_exact_end.plot("greedy_exact_end")

greedy_bi = greedy_bi_tsp(cities100)
puts greedy_bi.distance
greedy_bi.plot("greedy_bi")