69 lines
1.4 KiB
Crystal
69 lines
1.4 KiB
Crystal
require "./euler"
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module Euler
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class Prime
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include Iterator(NumType)
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def initialize()
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@sieve_size = 16
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@sieved_up_to = 0
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@primes = Array(Bool).new(@sieve_size, true)
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@primes[0] = false
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@primes[1] = false
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@index = 0
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iterative_eratosthenes_sieve
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end
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private def check_and_increase_sieve
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if @index > @primes.size - 1
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@sieve_size *= 2
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until @primes.size == @sieve_size
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@primes << true
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end
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end
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iterative_eratosthenes_sieve
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end
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private def iterative_eratosthenes_sieve
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2.step(to: Math.sqrt(@sieve_size)) do |i|
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if @primes[i]
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(i * i >= @sieved_up_to ? i * i : @sieved_up_to + i - (@sieved_up_to % i)).step(to: @sieve_size-1, by: i) do |j|
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@primes[j] = false
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end
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end
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end
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@sieved_up_to = @sieve_size-1
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end
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def next
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@index += 1
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check_and_increase_sieve
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until @primes[@index]
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@index += 1
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check_and_increase_sieve
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end
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@index
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end
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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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end
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end
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