27 lines
565 B
Crystal
27 lines
565 B
Crystal
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#wrong approach, should just do recursive trial division...
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def eratosthenes_sieve(n)
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sieve = Array.new(n + 1, true)
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sieve[0] = false
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sieve[1] = false
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2.step(to: Math.sqrt(n)) do |i|
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if sieve[i]
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(i * i).step(to: n, by: i) do |j|
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sieve[j] = false
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end
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end
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end
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result = sieve.map_with_index { |b, i| b ? i : nil }.compact
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end
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def prime_factors(n)
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nums = eratosthenes_sieve(n).select { |i| n % i == 0 }
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nums = nums + nums.map { |i| n / i }
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end
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puts eratosthenes_sieve(600851475143)
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puts prime_factors(600851475143).max
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