24 lines
551 B
Ruby
24 lines
551 B
Ruby
# frozen_string_literal: true
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def fft(input)
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base = [0, 1, 0, -1]
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input.each_with_index.map do |_n, i|
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pattern = base.flat_map { |e| [e] * (i + 1) }
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pattern *= (input.length.fdiv pattern.length).ceil + 1
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pattern.shift
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cross(input, pattern[0...input.length])
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end
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end
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def cross(input, pattern)
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total = input.zip(pattern).sum { |a, b| a * b }
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total.abs % 10
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end
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input = File.read(File.join(__dir__, 'input'))
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numbers = input.strip.split('').map(&:to_i)
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100.times do |_i|
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numbers = fft(numbers)
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end
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puts numbers[0, 8].join
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