Dijkstra's algorithm to search shortest path in Graph

dijkstra.rb

class Graph
  def initialize
    @graph = {
      "Odin"     => [["Thor", 1], ["Heimdall", 1]],
      "Fregg"    => [["Heimdall", 1], ["Thor", 1]],
      "Heimdall" => [["Odin", 1], ["Fregg", 1]],
      "Thor"     => [["Odin", 1], ["Loki", 1], ["Fregg", 1]],
      "Loki"     => [["Thor", 1]]
    }
  end

  def search(from, to)
    @from = from
    @to   = to

    travel_by(calculate_distances, from, to).reverse
  end

  def travel_by(distances, from, to)
    path = []
    path << to

    return path if from == to

    path += travel_by(distances, from, distances[to][0])
    path
  end

  def calculate_distances
    distance = 0
    unvisited = []
    distances = {}

    graph.each do |k, _v|
      unvisited << k
      distances[k] = ["", Float::INFINITY]
    end

    current = from

    while unvisited.length > 0
      neighbors = graph[current]
      neighbors.each do |node|
        node_name, node_length = node
        if (distance + node_length) <= distances[node_name][1]
          distances[node_name] = [current, distance + node_length]
        end
      end

      unvisited.delete(current)
      break if unvisited.length == 0

      unvisited.sort_by {|node| distances[node][1] }
      current = unvisited[0]
      distance = distances[current][1]
    end

    distances
  end

  private

  attr_accessor :graph
  attr_reader :from, :to
end