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42 lines
1.0 KiB
42 lines
1.0 KiB
3 years ago
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template, rules = ARGF.read.split("\n\n")
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template = template.chars
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rules = rules.scan(/(\w{2}) -> (\w)/).to_h
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# polymer = template
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# 10.times do
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# polymer = polymer.each_cons(2).flat_map {|a,b|
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# [a, rules.fetch("#{a}#{b}")]
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# } << polymer.last
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# end
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# min, max = polymer.tally.values.minmax
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# p max - min
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tally = Hash.new {|h,k|
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polymer, steps = k
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new_elements = polymer.each_cons(2).map(&:join).map { rules.fetch(_1) }
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h[k] = case steps
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when 1
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(polymer + new_elements).tally
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when (2..)
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initial = new_elements.tally.transform_values { -_1 }
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polymer.zip(new_elements)
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.flatten[0..-2]
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.each_cons(2)
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.map { h[[_1, steps-1]] }
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.inject(initial) {|final,tally| final.merge(tally) { _2 + _3 } }
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else
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fail
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end
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}
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final = tally[[template, 40]]
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# correct for internal elements being double-counted
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template[1..-2].each do
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final[_1] -= 1
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end
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min, max = final.values.minmax
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p max - min
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