deep_compact

class Array
  def deep_compact
    term = []
    hash = each_with_object({}) do |obj,res|
      if obj.is_a?(Hash)
        obj.each do |key,val|
          res[key] ||= []
          res[key] += val.respond_to?(:deep_compact) ? val.deep_compact : val
        end
      else
        term << obj
      end
    end
    hash.map {|it| Hash[*it] } + term
  end
end

CASES = [
  {
    INPUT: [
      {2=>[
        {8=>[
          {9=>[
            {3=>[]}]}
        ]},
        {8=>[
          {7=>[]}
        ]}
      ]},
    
      {1=>[
        {5=>[
          {7=>[]}
        ]}, 
        {3=>[
          {4=>[
            {5=>[
              {6=>[]}
            ]}
          ]}
        ]}
      ]}
    ],
    OUTPUT: [
      {2=>[
        {8=>[
          {9=>[
            {3=>[]}
          ]},
          {7=>[]}]}
        ]},
    
      {1=>[
        {5=>[
          {7=>[]}
        ]},
        {3=>[
          {4=>[
            {5=>[
              {6=>[]}
            ]}
          ]}
        ]}
      ]}
    ]
  },
  {
    INPUT: [
      {1 => [:a], 2 => [:b]},
      {1 => [:e], 3 => []},
      {1 => [:f], 2 => [:g]},
      {3 => [:x]}
    ],
    OUTPUT: [
      {1 => [:a, :e, :f]},
      {2 => [:b, :g]},
      {3 => [:x]},
    ]
  },
]

CASES.each_with_index do |it,idx|
  ok = it[:INPUT].deep_compact == it[:OUTPUT]
  puts "#{idx}: #{ok ? :OK : :FAIL}"
end