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def self.iterative_deepening_search(root, problem)
    fringe = [root]
    visited = []
    past_fringe = []
    until fringe.empty?
      vertex = fringe.pop

      visited << vertex
      past_fringe << vertex

      solution = problem[vertex]
      return solution if solution

      if fringe.empty?
        fringe = past_fringe.collect(&:neighbours).flatten - visited
        past_fringe = []
      end
    end
    false
  end
end