Try to make a hash stack in Ruby

output.txt

$ rbx stack.rb 
[4, 8, 12, 16, 20, 24, 28, 32, 36]
[{:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>nil,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>9,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>0,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>5,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>9,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>6,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>5,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>2,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]},
 {:done=>[9, 0, 5, 9, 6, 5, 2, 0],
  :last=>0,
  :cells=>[1, nil, 1, nil, nil, 1, 1, nil, nil, 1],
  :values=>[]}]

stack.rb

#!/usr/bin/env ruby
require 'pp'

stack=[]
stack.push( { :cells => (1..9).map{|i| nil }, :done => [], :last => nil, :values => [] } )
while stack.count < 9
  state = stack.last.dup
  state[:last] = rand(10)
  state[:cells][state[:last]] = 1
  state[:done] << state[:last]
  stack.push(state)
end

pp stack.map{|s| s.object_id}
pp stack