24 lines
438 B
Crystal
24 lines
438 B
Crystal
# miscellaneous stuff
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module Euler
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def self.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 self.palindrome?(x)
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x.to_s.reverse == x.to_s
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end
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end
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