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require "prime"
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instructions, network = ARGF.read.split("\n\n")
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network = network
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.scan(/(\w+) = \((\w+), (\w+)\)/)
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.to_h { [_1, { L: _2, R: _3 }] }
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steps = ->(start, finish) {
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node = start
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instructions.chars.map(&:to_sym)
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.cycle.with_index.lazy
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.filter_map {|dir, i|
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node = network.fetch(node).fetch(dir)
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(node =~ finish) ? i+1 : nil
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}
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.first
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}
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# part one
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p steps.("AAA", /ZZZ/)
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# part two
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nodes = network.keys.select { _1.end_with?(?A) }
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node_steps = nodes.map { steps.(_1, /Z$/) }
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p node_steps.inject(1, :lcm)
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