50 lines
821 B
Ruby
50 lines
821 B
Ruby
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require 'prime'
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def odd_composites
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enum = Enumerator.new do |y|
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a = 3
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loop do
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y << a unless Prime.prime?(a)
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a += 2
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end
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end
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enum
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end
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def squares
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enum = Enumerator.new do |y|
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n = 1
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loop do
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y << n ** 2
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n += 1
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end
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end
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enum
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end
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def find_sum(num)
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found = false
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primes = Prime::EratosthenesGenerator.new
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prime = 0
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squares_enum = squares
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while prime < num
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prime = primes.next
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squares_enum.rewind
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twice_square = squares_enum.next * 2
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while twice_square < num
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return [prime, twice_square / 2] if twice_square + prime == num
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twice_square = squares_enum.next * 2
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end
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end
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found
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end
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def property?(num)
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find_sum(num)
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end
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def find_incorrect_up_to(n)
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odd_composites.take_while { |x| x < n }.reject{ |x| property?(x) }
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end
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