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56 lines
1.1 KiB
56 lines
1.1 KiB
require "set"
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execute = ->(r, op, arg) {
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delta = case op
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when :acc
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{ acc: arg, pc: 1 }
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when :jmp
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{ pc: arg }
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when :nop
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{ pc: 1 }
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else
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fail
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end
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r.merge(delta) {|_, old, new| old + new }
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}
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# part 1
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seen = Set.new
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detect_loop = ->(r, op, arg) {
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throw :halt if seen.include?(r[:pc])
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seen << r[:pc]
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execute[r, op, arg]
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}
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instructions = ARGF.read.scan(/(\w+) ([-+]\d+)/).map {|op,arg| [op.to_sym, arg.to_i] }
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registers = Hash.new(0)
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swaps = { nop: :jmp, jmp: :nop }
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candidates = instructions.filter_map.with_index {|(op, arg), i|
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swap = swaps[op]
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if swap.nil?
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nil
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else
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[i, [swap, arg]]
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end
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}.map {|i, swap|
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candidate = instructions.clone
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candidate[i] = swap
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candidate
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}
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candidates.each do |candidate|
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seen = Set.new
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registers = Hash.new(0)
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catch(:halt) do
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while instruction = candidate[registers[:pc]]
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registers = detect_loop[registers, *instruction]
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end
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end
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break if registers[:pc] == candidate.size
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end
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p registers[:acc]
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